It's one of those days, lots of bloggin' :)
Callouts are great, there are a few drawbacks but in general, they're great. However, you might experience that they aren't triggering as they should. Well, first thing to check is that callout.config is correct. Does it work on some other system? I have noticed that there are some problems with wich version is set in the top part.
However, there might still be problems with callouts not triggering properly, this might be due to a reinstallation of CRM which actually shuts off callouts, and doesn't put them back on again. (shame on you installation developers!).
Have a look at the blog bellow for more info on how to put them back on again.
CRM and SharePoint Consultant