Search for "me" on Google (Google Profiles now in search results)
googleblog.blogspot.com
googleblog.blogspot.com
It becomes incredibly easy for spammers to pull these handles from public searches, add an '@gmail.com' and spam them.
If you add a really naive email hashing scheme to your profile pages, the spammer doesn't even have to send the email to see if it's valid!: http://www.cs.brown.edu/~cce/microid/
Nice lesson for all marketers - scaring users works :)
Other impressions: Needs gravatar support. I like that it pulls the favicon from your links.