As of now, whenever I want to download a mod the dreaded "server unreachable" came. Apart from that, NMM have difficulties managing multiple downloads. If you download 5 big mods at once, you are most likely fail the download. But NMM has great resume feature, so that you don't have to start over again. That feature is really great, and one of my factors in using NMM. NMM is the best thing for now, it's not really good, but it's the best. Apart from my small complaints, NMM works really good. I never have problem installing/uninstalling a mod using NMM. NMM really solve problems for people who don't understand how to mod manually. So in that sense, NMM has successfully solve a problem (helping user to mod), but they still need to improve on other factors.