Mail sync:
In my experience, Yahoo Mail (I have Yahoo SBC Global) is not the best when it comes to syncing with not only Android mail but also Outlook. Many times it doesn't sync from my PC with Outlook reliably. It tries to connect/sync but I get all sorts of timeout errors on the PC. Then if I try some time later, it works fine. Now this is not unique with Android. My prior smartphone running Windows Mobile Professional 6.1 also had issues with it.
On the other hand, I have a personal email account through GoDaddy, and neither Outlook on my PC, WinMo, nor Android mail on the Optimus have a problem with it.
Rob
Update: I forgot to mention that apparently Windows Phone 7 is also having issues with Yahoo mail as well.