Just a word of advice to anyone using a lot of mods...Export a backup your mod list in CKAN often.
I recently ruined my install by haphazardly updating after a long break, and had major problems trying to revert. But I realized I had some regular exports of my mod list.
If you do this, reverting is as easy as:
1. Backup the entire install as-is (broken).
2. Uninstall KSP and delete everything.
3. Install KSP fresh with version you want (Betas tab if you are using steam).
4. Install a fresh version of CKAN.
5. Import your old mod list file using the "install from .ckan" feature.
6. Copy over your old saves folder.
7. Startup KSP.
I was completely amazed how well this worked to get me back where I was 4 months ago. I loaded up my gargantuan space station with no problems at all (493 parts) and my interplanetary mothership (745 parts) with no problems.