Cox claims up to 3Mbit downstream on my connection, and best case that's about what I get--I think I've just bumped 400KB/s on large downloads from fast servers. (That CNet test showed 2.2Mbit, which at least isn't wildly innacurate.)
Upstream is only 256Kbit (32KB/s), and that's generally about what I get when I upload.
It seems like 3Mbit down/256Kbit up is sort of the US standard in most places these days; I've been looking at SBC DSL, and they claim 3Mbit/384Kbit for the same price as Cox's service. Rather on the slow side versus what you can get in Japan and Korea, but it's good enough for most uses.
Incidentally, Cox on their website claims some relatively strict restrictions on upstream and downstream bandwidth for their plans--in the vicinity of 30GB down/8-12GB up (per month) depending on how much you pay. That's why I was looking at SBC, which claims they put no caps on speeds in either direction, and have slightly higher upload cap for the same price.
I haven't been hassled by Cox for exceeding their caps so far (I don't think they're in force where I live, and it wasn't part of the agreement I signed up under), but I'm wondering if others have experience with these two ISPs (the only two high speed options in my area), and how draconian they are about speed and bandwidth caps in practice...