This morning I rooted my android G2x. The main motivation was curiosity, but there were a few things that I wanted to improve about my phone. T-Mobile didn’t pre-load too much junk onto the phone, but there was the T-Mobile app-pack and Mall, Nova and Tegra game stores, and the lite version of TeleNav. Also, to get a good ad-blocker you need to have root access.
So I took the plunge and rooted the phone. There was a point when I thought the phone was bricked, but it all worked out in the end.
Even without the mistakes that I made, I would say that the benefits do not justify the effort (at least for my phone). I am glad that I did it, but more for the experience than the end result.