If you've never used IFTTT before, give it a try. There are currently 50 "channels" on IFTTT, with everything from Twitter and Facebook to ESPN and weather. You create "recipes" that perform a certain action if a specific trigger is met. For example, I use a recipe that tweets the URL of every post that I write on TUAW from my Twitter account.
What does this have to do with WeMo? Well, there are IFTTT channels for the WeMo motion detector and switch. This opens up all sorts of possibilities. Say you want to receive a text message whenever your cat uses the litter pan. You set up a motion detector next to the litter pan, and every time el gato feels the need to go, you get tweeted.
There are even wilder things you can set up. Plug a fan into a WeMo switch, then set up an IFTTT recipe to turn the fan on if the local outside temperature goes above 85° F (I tried this — it works). Have IFTTT call you whenever someone enters the house (it works). And if you want to shut that fan off, you can either write another recipe or just use the WeMo app to shut it off remotely.
Read Sande's complete review:
Belkin's WeMo: iPhone-based home automation with a taste of IFTTT