It won't download any mods over half the time...it eithers says "file doesn't exist", when it does, or it just says error. WTF?

Either the poor excuse for servers is down, getting to much attention or it's just NMM being a horrible program. Just download the mods manually and use another mod manager, I'm sure there is another because NMM is horrendous.

Please do tell what other mod managers there are? This is how NMM is for myself as well and it's quite frustrating.

I expected there would be one that is like FOMM but apparently not, the closest is TESModmanager but from reading the comments it seems that is pretty damn buggy.

Download manually from the Nexus:

Select "Download (Manual)" from the mod page, and choose a server near you (or one with few users on it taking up bandwidth). Save the mod to your desktop or somewhere you'll find it.

If that server is too slow and you're downloading a huge fie on a slow connection then cancel that and choose a different server.

Open NMM from your start menu. Browse to the mods tab then click "add mod from file" (the jigsaw icon at the top left of the screen). Browse to your desktop (or wherever you saved the downloaded mod) and select this.

NMM will then install and manage as usual.

I never use the auto-download-and-install function of NMM, I find it too unreliable. Haven't yet had a problem with manual download then letting NMM install.

Well, they are replacing their servers at the moment, so it is possible that there are some problems I suppose...

http://www.nexusmods.com/games/news/12252/?

Also:

Yep, always manual download. jackstarr hit the nail on the head here.

Yes, but then NMM is rather useless. All mods will be in the unassigned category and NMM won't check for updates either. If I downloaded manually from Nexus I'd rather use Wrye Bash/BAIN as the installer than NMM.

NMM checks for updates for me, that is the only reason why I use it.

I have combined the NMM folder with Wrye Bash so that NMM checks for updates (manual download and install via add button). Close NMM and open Wrye Bash and make my installations and Bashed Patch.

This works very easily.