I bet Posterous have spent lots of time tweaking their "parser" to handle all kinds of weird mails sent from ancient clients. And many webapps could need a simple way receive mails from users, without dealing with this mess.
Posterous put a lot of energy into detecting & discarding fake emails. I remember this TechCrunch contest, challenging people to forge email headers to get onto Michael Arrington's Posterous:
Seems like this matters a lot less in a review website than in a social network/blog type site, but could still be an issue. I wonder if/how this site dealt with it.
Taking lazy registration one step further and going with no registration at all is a cool concept, as well. If you can center all of your functionality around email (or something else that already provides auth), it's possible.
When App Engine was released, I made an app called Lunchstr (http://lunchstr.appspot.com) just to play with GAE. The app isn't very useful, but the no-login, no-registration philosophy was kinda cool.
Is the no-login model the future? As application developers what do we lose by not requiring accounts? In most cases, isn't the account the doorway to income? How many more applications that don't have a revenue model out of the gates (including Twitter, Facebook, etc.) can the VC community support?
What about joining these two?