I have entered the Schengen Zone a large number of times without my US passport being stamped. Some EU passport control checkpoints even refuse to stamp my US passports, and others don't stamp it unless asked (and I don't ask usually). Some Schengen passport control staff stamp my US passports without even checking out the biodata info in my passport -- as happened to me again when entering Schengen a few days ago in a country with a Germanic language as the only official language.

Entering munich once and the officer just glanced at the cover of my passport and waved me through. I was like ugh... Ok?! Didn't even get a chance to hand it to him. Haha. Odd for the germans who are sticklers for rules. Thankfully no trouble leaving later.

That (show passport cover only) used to be the norm ZRH treatment for me on a U.S. passport, but that changed for me twice: after US passport cover redesign and separately after the Swiss became part of Schengen. Now they almost always open my passport to my biodata page.

Perhaps some passport control of countries bound by Dublin III don't want to catch people using counterfeit or genuine US passports in illegitimate or otherwise questionable ways? For example, maybe some Danes really want refugees/asylum-seekers entering at CPH not to be processed in Denmark and want them to file in Sweden? Maybe some Italians want fake/fraudulent US passport users to file in France or Germany? The incentives are rather mixed, and U.S. passport redesign won't do this dynamic any change.

Countries certainly have an interest in trying to protect the "trust" in the ID papers/docs which they issue, but at some point these redesigns of docs are more workfare than systemic solution to any material "trust" deficit in the collective of such documents.

At AMS, I've been told more than once that if I want to avoid filling up my US passport with stamps, to use my Dutch passport for entry and exit. After actually remembering to bring my Dutch passport, my US one is no longer at risk of being filled in less than 3 years. However once I made the mistake of entering on my Dutch passport and exiting with my US passport, and they couldn't find the (non-existing) entry stamp.

Also on validity - after much back and forth, the Dutch FINALLY went to a 10-year passport last year. I really hope the US doesn't go back to a 5 year passport. I've always found the 5 year an incredible nuisance because effectively means it is valid for only 4.5 years (taking into account validity requirements for entering many countries). If you want to make it less than 10, how about 7?

My passport expires in 2017. Would it be worth it to renew after my next international trip (I know I'll have at least a few month gap in international travel) so I can get another 10 year validity one?

There is no reason right n:ow to suspect that the US will change the length of validity of passports it issues.

There won't be any reduction in the validity period from ten years to five years that corresponds to the upcoming passport redesign and (eventual) price hike, but that may be subject to change.

About 2 years after the Swiss joined Schengen, I traveled from the U.S.
to Europe by sea(private yacht) and return by air(using miles). The port
immigration officer only looked at my US passport without even opening
it.(there were only 3 of us on the yacht, plus 5 crew) At the time, I did
not think too much of it. After 3 weeks in France and Netherlands, I went
to Zurich by train.(via Germany) My last week was in Geneva. The
lack of an entry stamp from any European country created a huge problem.
My U.S. passport was completely blank because I had just renewed it prior
to sailing from the US. The Swiss immigration officer demanded to know
why there was no record of me entering Europe, as well the lack of an
airline ticket or boarding pass showing how I got there. I explained how
I sailed on my friend's private yacht and that didn't sit too well with them.
They spent 30 minutes calling the French port officials who also couldn't
tell them anything. Finally, I remember that I had photos of the yacht
at the port. I showed the photos to the Swiss officers where were finally
convinced that I did not enter the EU illegally or overstayed.

I still sometimes get those immigration officers who do not stamp my
U.S. passport(for example, Stockholm and Barcelona) I now absolutely
insist that they stamp my passport with the entry date clearly visible. :)

They must not have liked something about you or what you said that goes beyond just the lack of entry stamp -- as the lack of entry stamp (and even electronic record) is a very frequent occurrence, more so in the summer, for Swiss exit passport control.

I've entered and been with others who entered without European stamps in U.S. passports and then flown from ZRH or GVA to North America; and we've never personally or professionally encountered such treatment in Switzerland. Then again, I don't claim to come into the Schengen zone by private, non-commercial boat, with anything or everything that it may imply.

Some Schengen countries refuse to stamp my US passport, and their staff even claim they are not allowed to stamp my US passport.

I have heard that from a passport checker at FRA. I assume there is no
actual law/regulations that says they can't stamp US passport.

Although I've also gotten that from Canadian AND U.S. immigration
officers at land border crossings in Detroit and Vermont.

Government employees making up non-existent rules seems to be
a worldwide thing. :D :D :D

How far in advance do they usually announce fee increases?

FRA? I have flown there numerous times, and my US passport was stamped every single time. That explanation was clearly a BS.

Canadians tend to not stamp US passports at land POEs. They actually get irritated if you ask them to do it. The last time I asked a CBSA lady at a remote land crossing (US-395) to stamp my US passport, she disappeared for 5 mins inside the building and then she stamped my passport and gave me only a week to be in Canada. This stamp with the unusually short stay authorisation apparently amused a CBP officer on the way back even though he did not ask explicitly about it.

They most commonly do indeed stamp US passports at FRA, but sometimes they refuse to stamp some U.S. passports of some admissible US passport users at FRA.

Well, as a resident here in Germany, they don't stamp my US passport, but I am surprised that visitor passports aren't stamped routinely. One of my friends even had to leave the sterile area because he forgot something, and he was stamped back into Germany, and then again back out, on the same day (2 out stamps and 1 in stamp on the same day...).

I've had that happen on my US passports too, but some Schengen passport control staff will simply invalidate my exit stamp while allowing me to go back to the Schengen side.