I had a cheap android phone from Walmart (Samsung Ex-II). I was getting sick of all the bloatware that T-Mobile put on it. I decided to chance bricking the phone and wiped it and put cyanogenmod on it instead.
Best decision I have ever made.
The phone went from sluggish to acceptable. The battery life went from about a day to 3 days or so. Plus there are a lot of interesting debug support features (if I ever get around to developing anything for it).
There was absolutely no downside to this.