Some things. Have you changed services recently? Do you download large files? What do you use the computers for? Is there some program you run which uses lots of bandwidth? (This could seriously decrease internet speed with a wireless router). Are there any times when the internet is faster than another time?
We have not changed services. We've been using Qwest DSL since late 2005.
I don't think I download large files. At least not frequently. I'm not sure how large is large, though. The occasional 8 page PDF is about the biggest I can think of.
We primarily use them for web browsing (including streaming short video segments), working on Excel documents, iTunes, and storing/editing photos.
If we run a program that uses a lot of bandwidth, it's a secret from me. From what I know, it seems like if anything we might be using a lot of system resources, but not bandwidth. But I'm not particularly knowledgeable about such things. We completely avoid file-sharing type things. We try to run a very clean ship.
The speed doesn't seem to vary greatly from one part of the day to the next. There have been 2 or 3 times (out of many dozens) when Hotmail loaded surprisingly quickly (~3 seconds), but I haven't seen any pattern.