I've been using phone + Strava for two years now because I'm cheap and kinda poor. It goes in a plastic bag in my jersey pocket, and I check the stats when I get home. It's pretty darn accurate compared to what others upload using Garmin on group rides and provides enough data to get started.

The Garmin Edge 20 and 25 look pretty nice, though, and I'm tempted to try one. The downsides of Strava on the phone for my purposes are (1) I have to remember to hit pause while stopping at a store or a washroom, and (2) since it's in my pocket, I have no idea how fast I'm going until after the ride. Getting a good idea of speed can be somewhat helpful for riding in organized groups and keeping a consistent pace, especially if it's windy.