I had serious connection issues a few weeks ago, comcast did a bunch of stuff, including running a new line to the house and after that my old Netgear RT314 was no longer compatible... or it got flaky, anyway, I replaced it with a Linksys WRT54G and during the interim, with JUST the modem to PC connection I speed tested and got 12257/349 kbps.
Now that I have the router in, I'm getting consistent 10084/351 kbps
This is talked about in a bunch of threads over at
dslreports.com
~~and I should point out that Comcast has been doing bursting for a while, making speed tests unreliable, best test is still a large file fast server download, like a linux distro or similar.