I'm pretty sure that there are many, but weight and compression braking come to mind. cornering is a little different from what I understand, but someone else who has had more experience on both could shed some light on it.
Good question. Unfortunately, I have never ridden one of the new Yamaha thumpers. I've heard they rev alot higher than the XR's that I'm used to, and handle better than a stock XR.
Regardless, I think the weight, compression braking and the torque down low are the biggest differences. It's hard to explain "how" to ride thumpers, you kinda have to get some time on one and adapt your own techniques.
Because of the torque and lower instantaneous wheel speed, you will get more traction on a thumper. This makes it harder to steer with your rear end by lighting up the rear wheel. When you factor in the weight, thumpers aren't near as easy to throw around as a 2-stoke.
The smooth power delivery of thumpers requires a smooth riding style, in my opinion. Like a race car, smooth, fast lines through turns and hard controlled braking are key to being fast. Good luck.
Incidentally, I ride a -00 YZ250 and had a ride on a friend's -00 YZ426F. I have also ridden CR5s, a Husaberg 501FC and KTM 380s pretty extensively.
Compared to the 250 the 426 has much smoother pull from low revs. It pulls cleanly, but not very powerfully at low revs. I never really got a chance to rev it out properly, but I have to say I was a bit unimpressed. Compared to the Husaberg or the big two-strokes, the grunt just wasn't there. However, the 426 was much easier to handle than the other big bikes.
I'm going for a KTM 520 SX probably this fall or next year at the latest, since I want all the low-end torque I can get. I'm pissed off at having to rev the 250 like a maniac, although it handles very well.
Roll the throttle on, don't whack it.
Never shut off going up a jump face, the compression braking will make you endo.
Roll off the throttle later and brake less, when entering corners. Or turn up the idle speed till you get used to it.
Don't down shift unless absolutely necessary. The beast will pull you out of the corner:)
Snaggle is correct, you'll have to ride the bike trough the turns, not slide it.
Ya, rolling the throttle is a must. Also, instead of just hitting the gas, it helps to "prime" it first. In other words, blip the throttle quickly, let off then roll the throttle on hard. It gets the RPM's up a bit, and gets the vacuum going for the big rush of fuel. I really had to do it on my XR200, but it still helps on my XR400. This trick also works good when you have to approach a hill slowly, blip it, then roll it on hard, and she will walk right up. Thumpers RULE! Good luck.