Kernel PPA

The Ubuntu Kernel team have a PPA which they maintain with the latest version of the kernel for Natty - having just checked, the current version in the repo is 2.6.39-0.5

Mainline Builds

If you want to test more vanilla Kernel Builds then the kernel team also do nightly builds as well as builds for each release candidate.

For example - the new v3 kernel builds are available - these are tagged as -oneric. Obviously these builds are specifically been built for the next version of ubuntu in mind. Also, if you install them, you'll need to keep up-to-date yourself.

Change info for Kernel 2.6.39

However - there is little point in upgrading a kernel unless you are having serious issues with you current official Natty kernel. What do you expect to gain?

Is it "safe and stable" - arguable terms. Linus T calls it stable. There are many thousands of users using 2.6.38 in Natty and many of the latest distros.

Linus produces a change-log for each kernel release. In my mind, this is a bit deep for me. There are a few sites, such as this, that explains what new changes are available a bit more clearly.