Any one speed measurement between your machine and any one particular server is pretty much meaningless; its just what it was between those two machines at that particular time. To really get an idea of what your actual limits are, you should run several tests over a fairly broad time period - like every day, a few times a day, for a week, and test with several different servers. The more measurements you make, to more servers, over more time, the more accurately you'll be able to calculate what you've really got for an average. Once you've got a solid average for a benchmark, you can begin to really tell what's going on with your connection and with other websites.
Check out the various speed and throughput tests at Numion.Com
. The website download stopwatch feature there is pretty neat - shows you just how long it takes any given web page you type in to load on your machine.
Oh, my ADSL connection is nominally 3M down, 512K up - it averages around 2.8M down, 480K up on straight speed tests, which is roughly consistent with stopwatch-timed FTP transfers of known-size files.
Except, of course, for when it crashes - the local telco has a way of screwing things up in most imaginative fashion.