Where can I get my mtg-cube critiqued?
The best place that I know of is http://www.reddit.com/r/mtgcube

Other options include tweeting the link to your cube with the hash tag #mtgcube.

Quite often if you do one or both of those, people will draft your cube using cubetutor, which will then give you drafting statistics about what cards are taken highest, and you'll usually get direct feedback from the person themselves as well.