Eraldi21 wrote...
found that it has something to do with youtube videos loading from my isp's server cache
From what I can tell, that is the correct answer. Check the location from which you downloaded the video. My ISP works similarly.
As you can see, IDM doesn't download from youtube proper, but rather, in my case, from http://o-o.preferred.rds-otp1.v13.lscache4.c.youtube.com/, the cache from the ISP server rds-otp1, RDS being my ISP and otp (Otopeni) being the location of the server.
Looking at animefreak's megaupload screenie, he's downloading from Megaupload, so it's obviously going to be slow(er). Besides, IDM can establish a great number of connections for just one download, so it's obviously going to download faster with it rather than when you simply watch it (download it with your browser).
Also, youtube allows you to make more than one connection, while some other sites do not (limited parallel downloads), which I presume was the case of Megaupload (can't check it now, but I'm pretty sure that's how it went), Rapidshare and most of the rest.(MediaFire allows multiple connections)
So that's why I think you can download at that speed only from youtube.