Random login issues upgrading to 1.0.8

[drmosh]

Most of the time users cannot login now after upgrading to 1.0.8... are sessions working correctly in 1.0.8?

Once in a blue moon all of a sudden they are able to login.

The version of Apache or PHP doesn't seem to matter either.

[J. Williams]

Have you checked its not mod_security causing problems?
Have you checked they've cleared their cookies and cache?

Sessions should work unless something required is missing