I'm using T3D v3, although v2.1 was 100% stable on my machine and never crashed. I really like the interface and the new stuff in v3.
I've rarely had any "real crashes" with T3D v3 either, but I've run into the "Do you really want to quit"-bug quite a few times (where the quit requster pops-up and you can't get rid of it). Also I've run into some error requesters which were impossible to get rid of.
I just avoid some of the modelling tools (the more advanced ones) and then it works pretty good, sure you should save once in a while when modelling just to be on the safe side.
The bugs I've encountered is mostly when using the modelling stuff.. when staging or making animation it's stable and also when rendering. I've made several animations with more than 800 frames with no real problems.. and the results
are very good.
Another important thing to keep in mind with T3D is to have quite alot of free memory available, if it runs out of memory you're facing a reboot. With more advanced scenes you should have at least 32MB ram free, preferrably 64MB or more when you start rendering.
My system is a A3k CSPPC 604e@200Mhz + 060@50Mhz with 96MB of Ram, a CVisionPPC and some other nice goodies

On this machine it often takes between 20-60s for a frame at 800x600 resolution... it churns out animations really fast. And if you want fast previews without anitalias you can get a frame rendered in 1-5s... ideal for previews of long animations.
Also regarding the dongle. I've never had any problems using T3D becasue of the dongle. But I've had problems with playing Payback (the game) with the dongle connected.
Another thing to note is that the cracked version of T3D v3 that was floating around is/was very very unstable... and doesn't reflect to real product's stability.