I only have 2Mbit, but at least it is 2Mbit both up and down :p
The biggest issue with ADSL is when the ammount of ACK messages going upstream fills up the pipe, so you get lousy download speed as well. This typically happens in filesharing scenarious where there's a large number of peers to send ACKs to all the time, or when you have multiple machines online at once, each generating lots of outbound traffic in terms of requests and ACKs.
