I did some reseach today on my problem, and it looks like the Atheros L1 driver that comes with Windows 7 and Windows Update is just a lot of crap. If I had a continuing ping going towards the ASG 7.902 everything looked fine until I started uTorrent and loaded a few torrent files, then I got lots of packet drops, ping timeouts etc. Lots of posts on the net about it. I changed to the 2.0.6000 driver for Vista (x64) and suddenly it looks much better for me and my computer.
can you please take a look at the packetfilter.log and check if you see dropped packets with a dstport=8080 at the same time where the http proxy stops working for you?