Hi horizonod,
Download speed depends on your connection speed, host(s) connection speed, how many hosts you're downloading from, network congestion etc.
Don't forget that you're downloading from other users, so if a file sits doing nothing for days it can be because there aren't any hosts online sharing the file, or the hosts online don't have any free upload slots. Click on the file within search results > search more > get more results...sometimes that can kickstart a stuck download. Or try a completely new search.
There are heaps of fake files around. These will sit connecting for ages & then get stuck needing sources forever. They'll never download. Always check a video file before download with Bitzi (try for audio as well, but music isn't rated as often as video). If the file's been rated, you'll get an idea of content & quality. If a file has heaps of sources but no Bitzi rating, chances are it's a fake. Check out the threads below for more info & tips, including how to use Bitzi
Fake files showing up in search results How to find music(tips for video as well)