There are some known bugs which invoke this behaviour.
For me I know that I must avoid the manual lens correction scale slider. If I use that, it will crash.
If I stay away from that, I have quite long sessions with LR4 beta1.
Paolo, do you indeed KNOW something about a beta2 not happening, because LR4-final will be the next?
I have seen this in several threads, but considered it a rumour.
Remembering the LR3beta-phase I neither knew in advance if the next version would be another beta or the final.
Personally I would appreciate if this is not set in stone in advance, but gets shaped along with the beta feedback from users.
Only then you really get the indicators about maturity or further opportunities to design a package people will be willing to pay for an upgrade.