Have there been any issues or problems noted with avast 6.0?
What are you expecting? Of course there have been issues noted. As have with notepad.exe, adobe reader, firefox, and zillions of other programs, be they small or large, complicated or simple.
There are 125 million avast users, so there are 125 million different PC setups concerning operation system, tweaking progs, unknown malware infection, hardware issues and, and, and... I estimate that at least 98% of all problems noted have their cause in individual PC setups and not in Avast bugs.
Avast 6 is a superb program, stable and mature and as far as I can judge bug free and you will most probably encounter no problems at all.
However: update your Win XP to SP3 and the IE to version 8 first.