I don't use a bike computer, but my iPhone app (Cyctastic) is great (shows time, distance, GPS, etc). It does eat up the battery, so I bought an external battery and keep it in a small bag. That allows me to go on 50-milers with no fear of running out of juice. And when it rains, I simply wrap a small plastic bag on the phone to waterproof it.
FYI - I don't care about weight, aerodynamics, etc, as I bike only for crosstraining and am not anal about the metrics.