Avast Home 4.8.1282 is working fine on two XP Home SP3 computers.
A few casual observations:
1) ashWebSv.exe appears to use significantly less memory
2) when I open Thunderbird and check my email, the mail scanner icon disappears after all of the emails are downloaded. When I check newsgroups (specifically grc.com) using Thunderbird, the mail scanner icon appears and will not go away even after I have left the newsgroups and moved back to my Inbox. I'm not sure if this occurred in previous versions and/or it's working as designed.
3) my upload/outbound speed appears to be noticeably faster using Avast versus a well-known and respected competitor (both using default settings) known for being light on resources. I used
http://ndt.itcc.unc.edu:7123/ and
http://speakeasy.net/speedtest/ to test on the same machine: Avast - 2.0 Mbps Competitor - 1.5 Mbps. Download speeds are the same.