One month after Google's cease-and-desist action, the popular custom CyanogenMOD Android firmware has hit a stable, presumably legal release point. It's as up-to-date as you can get on an Android phone, and it nearly fixes a seriously annoying slowdown issue.
Unlike the early CyanogenMOD releases, Steve Kondik's 4.1 and later releases don't use their own Gmail, Google Maps and other Google-provided, proprietary applications — they back them up from your current phone firmware, so you'll need to perform a phone data wipe to install. Luckily, the rooting/mod community has built a helpful wiki with installation instructions and troubleshooting help.
I've been using 4.2.1 for three days, and it does feel fairly stable — as stable as a stock Android installation felt, anyways, and a good bit speedier. The notable improvement is a default option to keep the "Home" app locked into your freed-up memory, eliminating the often painful home page refresh times sometimes found when quitting out of an application. All the standard warnings about modifying your phone's firmware and breaking your warranty apply, of course, but if you were looking for a good point to jump in, 4.2.1 seems worth it.