In the last week, the team has released 3 times.

1) SQL Developer 1.1.3 was released
2) Jdev 11 Preview was released where sqldev is built in
3) SQL Developer Migrations EA #2 was minutes ago posted. If your running 1.1.3, you'll see the update balloon soon.

However, I looked up some stats on usage and the majority of people are using 1.0.0 which was release March 2006. Here's the release notes for 1.1.3 so you can see what your missing.