Just got back from a 2 hr ride on some local singletrack, so I can give you my initial impressions.
For reference, I'm 210#, and moved from a San Andreas DHS w/ 6" travel in the rear. The SA was a great bike, and would mow over just about anything in its path. I found it made me a bit of a lazy rider when riding technical stuff & downhills, but that made it alot of fun!
The downside was climbing or out-of-the-saddle cranking. A great bike, but not the most efficient for either, which made it a bit of a chore on my local (steep) trails.
Now my impressions of the Yeti and the Pike:
The 575 is stiff and efficient. This was made clear to me by the fact that I was able to clean rocky climbs I'd never even gotten close to cleaning before, and use higher gears than I would normally use everywhere else. A+ there.
No problems whatsoever with the agressive stuff. I searched out a few tough rock gardens just to test this out, and had no problems. One item of note, though: The fact that it is stiffer and more XC-ish than my DHS did cause me to have one pretty big endo in a steep, downhill rock garden. Remember my comment about laziness in my riding style? Well, I do have to pay a bit more attention with this bike. (I'm not sure what you're riding now, so your mileage may vary.) That is not to say that it can't handle the abuse, though.
The Pike is a bit tall for the 575 fully extended, at least for tight singletrack. I felt the front washing in one dry and dusty section, so I dialed it down to 130mm and that solved the problem. I like the bump absorption and stifness of the pike, and the "coosh coosh" sound of the waste gate as you bang over roots is pretty fun, too.
Long and short? I'm extremely happy I bought this frame, and would recommend it to a fellow clydesdale.
