Alright, here are my experiences:
Background: YZ250 with well sorted suspension - Smart Performance (Dave's) setup, correctly sprung, Running about 102mm sag
Terrain: I switch between hardpack, shallow sand and deep sand. On hardpack I ride everything from flowing singletrack, to seriously rutted, rooty, choppy singletrack. In the sand, I'll ride flowing stuff and seriously whooped out deep sand. All offroad riding, no MX
I've been running stock offset for years, however I've shifted to the 22.5mm clams for the last 6 months.
Overall I'm very happy with the 22.5's. Coupled with less sag (closer to 100mm), the bike turns beautifully. Recently started running Pirelli MXMS front (always ran the MX51 and 756 previously). On the snottiest hardpack, slick red clay this bike turns on a dime. The Pirelli makes this thing stick like shit to a blanket. You can tip the bike into turns further. Under gas, the front easily out grips the rear (MX51 on the back). I wouldn't say that I've sacrificed any stability at all. Like I said, I ride some pretty nasty, choppy terrain. The bike inspires absolute confidence. Hit braking / accellaration bumps, logs, roots at weird angles and the whole bike tracks beautifully - no different to stock offset. It just turns better. The bike maintains its characteristic 'Yamaha Stability' - I ooze confidence in this stuff and its all thanks to the bike (at least coming off a KTM )
In the sand, the bike continues to turn better than before. I often find myself countersteering in ruts - it turns that well. I can rail berms better than before and don't feel the need to drag the rear brake as much through flat corners.
In deep whoops the bike maintains stability.
There is indeed less room for error - this applies to deep sand in particular. The bars will return to center faster than with stock offset. They'll snap to center rather than drift to center - if that makes sense. I don't find that this is a problem. The bars don't feel nervous, just more responsive.
There is a definite threshold though, with respect to bar position. Up to a certain point of rotation, the bars will snap to centre (as described above). Beyond this threshold, the bars will do the opposite thing - they'll snap to full lock. This takes place when you get sloppy with your steering input. If your smashing whoops and land with your weight too far forward and the bars cocked too far, they'll snap to full lock and spit you over the front. Yep, I've done that a few times now
Provided YOU don't get sloppy with front wheel placement and carry your weight back you won't get this problem. I like to kiss the top of whoops with my front wheel. Previously I didn't have to be so precise with where my bars were positioned when the front wheel hit the ground - it was a little more forgiving. Now I have to make sure I hold the bars straighter when hitting the tops of whoops (or when cornering through whoop sections).
On hardpack, I've had a few over the bars excursions, under really really heavy brakes (normally because I haven't looked far enough ahead and spotted that tree across the track ) the front can knife underneath you if you carry your weight too far forward with the bars turned a little. Once again, this is rider error.
Overall, I'm much happier with the 22.5's. Just carry your weight back further under heavy brakes and when riding whoops. When the bike gets air and eventually lands, make sure the bars are pointing straight(er). There is less room for error.
I've picked up a lot of speed in corners. Given that I ride predominantly single trail this has been of considerable benefit.
I can't stress enough just how good this thing is on slick hardpack when using the Pirelli MXMS in conjunction with the 22.5's. It feels like I'm cheating every time I hit a corner - its deadset criminal
I've found it necessary to add a little extra compression to the front end. The bars don't snap as easily when the bike is held further up in the stroke on the front. Coupled with greater rear weight bias (on fast stuff and under brakes) its pretty hard to go wrong with the 22.5's. Many of my 'over the bars' experiences come down to 'retraining' my brain. I'm so used to riding with the standard offset, I simply have to adjust to the new offset. I'm almost at one with the machine on this one now