After updating vbox today I got crashes on login with two different Win7 guests (gentoo ~amd64 host).
Luckily, only the most recent snapshot crashed and I was able to boot normally with the second most recent snapshot (both guests). I didn't lose anything important because the only thing I use Windows for is to run Windows Update :) (know thine enemy, etc) Maybe if you have important stuff on a Win7 guest you should make an extra snapshot just before you update to vbox-4.2.8 in case you need to delete the last one. BTW, I had no problems with linux guests so far.
