I think that's one of the exciting things Fridge has done:
Provide one of the killer apps of Google Wave — things like planning a trip with friends and sharing the photos afterwards — but with e-mail integration, not in a walled garden and without all the extra cruft Wave added (threading, branching and histories).
Is the fancy Wave stuff cool for hackers? Maybe. Is it good in a product? No. I'd go far as to say Wave is to Fridge as Linux is to OS X -- Wave might be important, but not in actually using it :)