Cadence is very useful, it is really good to help keep you from pushing too big of a gear, especially when you get tired.

And GPS is great - I was skeptical at first, but I really enjoy looking back at all the places I've ridden over the past three years since I've been using the Garmin (now a 500). You can post on the Garmin Connect site and share for free or if you're more competitive minded, try Strava, which automatically identifies climbs and other segments and compares your ride with other members of the service.

If you have a smartphone, you can probably get a free (or cheap) application that will do the GPS for you (including speed and distance). The only problem is battery life if you ride longer than a couple of hours. Strava offers one of these.

I must add - leaving all this at home occasionally and going for a fun spin around town is probably the best!