Hi
Perhaps, you should elaborate. I haven't seen an issue with cover art being displayed or not being displayed at all when using iOS 5, or even recall such an issue in previous iOS versions.
Some questions that comes to mind:
Which iDevice (iPhone 4, 3G iPod touch, iPad, ...)?
What specific iOS version is your iDevice running?
What app are you using (iPod / Music or third-party)?
What format are the songs in (AAC M4A, Lossless M4A, MP3, WAV, ...)?
What app was used to transfer the songs to your iDevice (iTunes, an iOS app, ...)?
How many songs are in your music library?
Are the songs of concern purchased from the iTunes Store, Amazon, etc or copied from CDs?
Have you tried restarting your iDevice?
Have you tried doing a fresh sync?
Have you checked for proper cover art application / display in iTunes?
Have you tried restoring to the most recent backup?
Regarding developer / beta versions of iOS. Well, they're in beta, so they may have issues, and you aren't even allowed to discuss them in public (NDA).