I recently upgraded a Motorola Defy to use CyanogenMod 7.2 as Motorola was not going to upgrade the phone from Froyo to Gingerbread. While the upgrade went reasonably smoothly and the phone is working well albeit with a few quirks, there was a major issue that I ran into recently. The phone loses its signal when it's roaming. Fixing this basically involves installing an (unsigned) app named Baseband Switcher, and setting the correct baseband for the phone.
There might be a newer version of the app. If you're reading this post far in the future (where I'm hopefully bathed every day in asses' milk), you might want to search for more recent releases.