Yeah, that is the thing to read (scottcraft post). It's not really that hard, and to be honest, the best thing for me is the custom themes and colors. You have access to the Bazaar Marketplace, which gives you things like ports of Chrome and Opera mobile browsers. You can also find a Trophy rom for Tango, but it looks like there are just a couple minor issues and I am waiting until those get solved.
I wouldn't say that there is any performance difference, but my phone sure looks better with different colors and themes. However, it seems to some that the Tango rom is a bit faster and may have better battery life.
Oh, forgot. You get a wifi hotspot too. Works good.