I have a Garmin etrex that I got five or six years ago. No maps, but it has waypoints. Handles speed, distance, compass as well as the data from GPS - elevation, time, sunrise/sunset. I got a handlebar mount last summer. I've used a bike computer before too.

GPS does everything a bike computer does, but I don't use it nearly as often. It takes some time to lock on to satellites, so it's no good for short trips. It's heavier to carry around if I lock up and go inside somewhere, and it's more valuable for someone to steal. It's not made to be a bike computer, so there can be a lot of awkward button presses to get to the numbers you want.

It's nice to not have to worry about a sensor or calibration though.

Since it doesn't have maps, the most I get is an arrow. If you've played GTA1 or 2, you know how that can mess you up. If you rely on it for directions, you can wind up on bad roads or dead ends. It's nice to have a destination, though - I can input latitude and longitude from Google Maps and it will point me exactly to that spot I saw on the satellite view.