Is it reasonable to use the Surface Pro 3 as a replacement for my Lenovo X201? I was looking at getting an X1 or a X240 as a replacement but if the Surface Pro 3 can do as much and be functional as a tablet as well I figure why not? I'd primarily be running MS Office, web browsing with Chrome and SAS statistical software.

Also any thoughts on whether I should wait until the Surface Pro 4?

I have to say, I'm surprised how much I like the SP3, having traded in my Lenovo TP410 because keys were sticking and I was just tired of lugging the extra weight and size in my carry-on.

As I mentioned above, I get about 5 hours of work time on battery. The glass screen is crisp with brilliant colors but the reflection is annoying at times. Windows 8.1 took quite a bit of getting used to, and I miss some of the gadgets of Win7. I was disappointed that much of the software I owned doesn't play well with Win 8.1 causing me to pay $$ to upgrade when there was nothing wrong with the software version I was using. Same with the Okidata printer I have - originally on XP, I downloaded the Win7 driver so it works but with quirks.

Some people thought the keyboard is a little "bouncy" but compared to the sluggishness of my TP keypad, I think it flies along quite nicely.

I have come to love the pen and touch screen for work stuff. I write a lot of documents with Word and Quark XPress, and modify and annotate photos with Photoshop. I've not used a tablet before so all that was new to me. I am now a fan :)

At home I do use the docking station (which is slick) and a monitor. Use the SP3 itself when traveling.

Don't know much about the SP4. Although, Win10 might be worth waiting for since I've read they will be bringing back the start screen.

The only thing I absolutely don't like about the SP3 is the invasiveness of Microsoft. Took me quite a while before I figured out all the "apps" and products it signed me up for and shared my account information with, so I could turn off access and delete personal information. Bloatware of a different sort.

So yes, I do think it can be a replacement for a laptop. It is for me.

At work, I used to exclusively use business ultrabooks. This time, IT gave me a choice of 3 replacements, one of which was the SP3. I've got to say, I also love it. Does everything my ultrabook did but in a much tighter form factor. Add in the docking station and it's a full-on desktop.

On a recent biz trip, person sitting next to me on the plane commented how impressive the SP3 seemed just by watching me, as she was using her older HP laptop.

No idea about SP4.

Try the keyboard out in person, which is the one questionable bit of ergonomics, especially compared to the Lenovos.

Whichever machine you look at, make sure you get the i5 (or i7) version not the i3, which may be slower than you're used to; the current-generation ultrabook i3s are really slow, potentially even compared to a 5 year old i5 in the X201 (they will outperform an i3 of that age, but by a surprisingly small margin.)

The Surface Pro 3 is a laptop.
Microsoft markets it as "a tablet that can replace you laptop", it should be marketed as "a laptop that can replace your tablet".

It has all the guts and capabilities of a laptop, plus an active stylus, plus the ability to operate as a tablet.
The only thing you compromise on (and only a little bit) is they keyboard, and I find the Surface keyboard to be better than many laptops out there.

I first got a Lenovo Yoga Pro due to the exceptional Lenovo keyboards. I parked the Lenovo becuase of the much lighter weight, much thinner profile, better screen, and infinitely better stylus of the Surface.

I run an IT Department, so I have free choice on what device I can use. I usually try every new type of device that comes out. I currently use a Lenovo X240, had an X201 before that, and various other models prior to that. I tried the Surface Pro when it first came out, as well as the latest SP3. After a month I gave up on it, and went back to the Lenovo ultrabook.

The reason it didn't work for me, is that when I'm doing work, at the office or at home, I need a full keyboard and separate mouse. When at home relaxing on the couch, using the SP3 as a web browser, the device is just too heavy to use comfortably. To me, it's not as good as a full blown laptop, and it's too much to be considered a replacement for a lighter/smaller tablet.

That's good advice. I'll go find somewhere local that I can check out the keyboard. I have to say when I tried the x240 keyboard I didn't care for the keys.

That is one of my concerns too although I plan on using a docking station if I'm actually stationary in the office or at home with a separate keyboard, mouse and monitor. It's only if I happen to be out that I'd plan on using the SP3 keyboard cover. I've had the same issue trying to use an Ipad around the house, it just gets too heavy to comfortably hold for reading after some point in time.

Same here.
I have Surface docking stations at my home office, and at my customer site office, each with 26" monitors and wireless keyboards/mice. At customer site, it runs through a KVM switch with three different computers.