I am thinking of renting a real-time GPS tracking unit for IM CdA to keep my family informed of my location. Thoughts? Recommendations?

Are the units too heavy or annoying?

The one I've seen so far is http://www.myathletelive.com/

I've read about Garmin's new device, such as the GTU 10, which is well reviewed but pricey. The upshot, however, is you can put it on your bike when it's shipped (or luggage or whatever) and be able to find it if it gets lost. Good luck! -- Katie

If you have a smartphone, you can use google latitude (google it :P ) and if you give permissions to your friends they can track you from a computer or their smartphone. Its really quite convenient and completely free.

A friend of mine (and fellow dctri-er) did this for his first ironman, and other than losing a handful of seconds in T1 fumbling with the phone it worked perfectly.

In fact, you had friends watching you and they turned on google latitude, you could even track where they were on the course so you could look out for them.