Good idea, a few problems in implementation Rated 4 out of 5 stars
Previously, I gave this add-on five stars because it solves a common problem (keeping Google from knowing who you are, without having to use Tor which Google seems to have blacklisted). However, I have to drop that to four stars because there's a fairly annoying problem with how it does it. The normal Google cookie is replaced by a randomized GS version, but local search settings are NOT preserved. Things like how many results per page, what layout of Google Image Search to use (it keeps switching from the "everything on one page" to "20 results per page, you have to keep clicking to see more"), and most annoyingly of all, it won't let me disable Google Instant!
If Moxie ever gets around to making a true update of the add-on (besides the versionbump that others have already done), I would really like to have a second options menu that lets me choose what search settings I want (and have it apply to all proxy addresses, rather than setting them individually).
Absolutely Essential Rated 5 out of 5 stars
This and AdBlock Plus are probably the top two add-ons that should come pre-installed with Firefox. It makes me mad that Google automatically logs me in/out when I log in to YouTube, so I have to delete the cookie manually, but this keeps the Big G from seeing me even after I do that.
Two minor recommendations, though: Make it easier to get alternate proxy servers (the default one was actually blocked by Google for a while, so I had to do the ironic thing and google "alternate GoogleSharing proxy servers"), and please update it for FF 7.0.1. I may have to downgrade back to 3.6.23 just to use it again...