I have 64k ISDN, and use FlashGet.
Very useful. Not really for download speeds - no difference noticed here, actually is better to make it use a single stream' multi steams afaik are for broadbander's to get around fileserver's rate limitations.
The best thing though, by far, is the ability to resume downloading. Even if your original host dies or whatever, you can usually find another one and flashget will detect it as a mirror and resume it from there. Another thing i like about flashget is it seems to give itself low priority over your bandwidth - if i open a webpage while DLing the page opens slower than normal but waay quicker than normal whilst downloading. Further, flashget has options to redial + resume if the line drops, disconnect (even shutdown the pc) once the download is done...
Very useful programs if you download anything big. I've got several fairly large D3/HL2 movie clips with it, and even the 100mb Enemy Territory Test and sometime after that, the 200mb Enemy Territory full game with it. With the latter two I started it downloading then returned the next day and it was done, flashget redialled every 2 hours when my ISP disconected me, shutdown the PC and everthing

when downloading huge files in this way its strongly advised to point flashget at a couple of mirrors to resume from should your original one have some issue or whatever.