Alright, I have some interesting good news to report after successfully installing the Beta with no notable problems.
According to this thread:
http://forum.avast.com/index.php?topic=33852.0 the problems I had with loading/streaming Flash-based videos causing some minor lag and unresponsiveness has indeed been fixed!!
I've tried reproducing this multiple times, and it seems that everything runs smoothly and closes smoothly as it should. (Before there would sometimes be delay where you could hear sound/music still playing for 1 second or so right when applications like Winamp actively playing music or FireFox actively streaming a video were closed--now it cuts out appropriately without any notable problems or delay).
Also, although I have not done extensive attempts to reproduce this, several old error messages I used to get as described in this thread:
http://forum.avast.com/index.php?topic=33052.0 seem to no longer appear! I tried to clear the Cache via Firefox's built-in function and it did so instantly and smoothly with no delay. CCleaner similarly has not done anything odd with suddenly reopening or closing while cleaning and has also not produced any error messages as it sometimes would. However, I cannot close this issue yet and will see if I can reproduce the problem or not some more (it was a relatively unstable one to pinpoint that could vary depending on the cache size I believe, so this may take a while longer).
As for some odd things I've noticed: the first one is that even upon boot-up it seems that the HDD activity is short for a while then suddenly gets very high again for a very, very long time. I'm not sure if this is the rootkit boot-time scan for avast! though, but when viewing the Vista Performance Manager, it looked like the real things reading/writing at that moment were the a LOT of images labeled as "svchost" reading/writing various files. I think it's more or less a Vista issue here or something situational since it was the first boot-up after the beta was installed---I think I'm going to have to test this more before I can confirm it to be an avast! problem or not.
The second and last thing I can note is that my HDD light blinks every now and then (around 5-10 second intervals). Unfortunately I can't confirm if this is normal and if it happened earlier on before the beta install, but it happens and bothers me a bit. Disabling avast!'s providers doesn't affect this though, and upon viewing the Vista Performance Manager revealed that there were still quite a few images labeled as "System" reading/writing various files--so my guess is that this was probably something normal for Vista.
Other than these reports so far everything's been running fine--many thanks to the avast team! I'll post another report sometime soon to further clarify if some of these issues are fully fixed or not as testing isn't entirely done yet.
P.S Sorry for the long post
and BTW I love the new context menu icon!
EDIT: Almost forgot to mention that there are 2 minor bugs that should probably be fixed in the final release. After installing the beta, my settings were changed from High to Custom because the Instant Messaging Scanner had the program "QQ" unchecked from its scanning list. Also the program "Utorrent" is still unchecked from the scanning list in the P2P scanner, and has been like this in 4.7 as well. Checking it changes the settings to Custom, and I think it should be auto-checked already with High settings instead.
