SEA has a reputation for going a little overboard (well sometimes completely nuts) over carry-ons. At least they tend to give a 'pass' to F and Elite customers with marginal bags (bigger than the sizer, but not monster sized). Honestly it does not make the boarding process go any faster there - I don't know what it is about SEA, but people there board like their feet are encased in cement and they're clueless about what to do when they find their seat (if they can even find it).

If your bag is marginal and can honestly fit in the overhead lengthwise without taking up space from other customers, let them tag it, then yank the tag while you're in the jetway and take it onboard - but you better make sure it fits properly.

I am glad to hear they were protecting the ELR seats - that was a pet peeve of mine from before. Are you sure they blocked people from changing to *any* open seat, or just the exit/bulkhead rows?