I think my biggest barrier in class was in learning the more advanced moves... I always felt guilty for being a bigger girl (size 16), and having the instructor have to push my extra weight up the pole when learning an invert or a climb...
Beyond that, I never really noticed if I was the biggest girl in my class... but some of my classmates did tell me later on when I was the first one to brave the pole shorts and a tank top on the very first day of class (and do so with confidence, might I add!), that I inspired them to open up and "strip down" (to pole shorts) as well...
As for accomplishing certain tricks, I don't feel that spins are really that affected by a girls weight... in class there were several spins that most everyone else got that I just could not get (at S it was the ballerina... I think at Veena it's called the front hook), but then there were other tricks that completely clicked... and had little or nothing to do with weight or size... everyone's body moves differently, and anybody, plus sized, or micro sized, has to figure out in which plane or frame of mind their body WANTS to move... I can now do the ballerina, but it will never be **MY** move and will always feel awkward and unnatural because that's not how my body wants to spin...
Transitions: not even a problem! More so than the skinny girls in my class, I actually excelled at floorwork and transitions... but I have a strong dance background, so I may have to be ejected from this topic... :P
Conditioning: S Factor has a phenomenal warmup with each class, and I really found that sufficed... I progressed at just about the same rate as the rest of my class with minimal modifications (though, the plank just is not my friend and my butt just refuses to lift off the mat! :P)
I will agree that split grip moves are more difficult, but as a pole-lefty, and with nerve damage to my left arm, I can't tell if it's more difficult because of that silly ulnar nerve of mine, or from the weight... And, might I add... I have a VERY loose right shoulder (I roll over in bed and it dislocates), and even when I was initially learning as a pole-righty, I never felt that I might pop it out or do any damage because of my weight... the body knows how and when to compensate... :)
I hope this helps... :)