Since NetworkManager (and all of the attached parts; VPN plugins, clients, backend...) is such a complex system, we're always looking for people to help out in whichever way they can.
One of the things I'd like to focus on this cycle (even if this announcement should have come long ago), is test cases and generally getting a good grasp of what works and what doesn't with NM, the clients, or plugins. Test cases are useful for us to know that things are performing as they should and even more important where development snapshots are involved, given the "in flux" nature of the code we're providing users. It's not that it's unstable code really (in fact, it's clearly not... 0.8 is now a stable branch that got tons of bug fixes, and seems rock solid if I believe the type and number of reports we get). Still, I'm interested to know about failures. That's partly why I wrote a number of test cases on the Desktop Testing Team tracker. There's a need for more though, and that's where the help of the community comes in.
If you know of some things that are important to you in NetworkManager, nm-applet, or the VPN plugins, write test cases for them! It will help everyone make sure those remain working, iron out the small annoying bugs, and just improve on the overall usefulness of NetworkManager.
Obviously, test cases and testing isn't the only place you can help. Are you annoyed at some little thing that works, but you'd love for it to go one step further in providing an amazing experience? Then we need you.
It's also very much the way I started contributing to Ubuntu, dealing with small annoyances which would make my life easier in using the desktop every day... And it was as simple and providing support for saving group or user password for the VPNC plugin.
I can already think of a few more of these small things, such as hiding the SIM PIN when prompted for it (since it's a password)...
I've started identifying small (but important!) bugs like this in Launchpad. As for other projects, look for the 'bitesize' tag. Here's an example.
They may not all be tagged bitesize, but if there's something that almost works for you and you want to take a look at fixing it, jump in! We'll all be glad you did. The same principle applies to many of the bugs marked as Wishlist, which are good ideas, maybe some need more discussion upstream, but they are all ready to be worked on (and have varying degrees of difficulty).
If you're looking to work on NM, the first thing you may want to look at is the wiki at http://live.gnome.org/NetworkManager. It's generally also a good idea to subscribe to the mailing list (see the previous link), so you can discuss changes with the community at large. Finally, there's truly no place more useful than the DebuggingTips page even for non-technical users. It's where you can poke NetworkManager to tell you exactly what goes on. In. Details.
In the cases where changes can be reasonably integrated into Ubuntu and/or Debian directly, feel free to submit merge requests and patches. This includes helping out fixing issues in the growing indicator patch for the applet :)
Finally if you're just curious and want to help out, you should know that there is a lot of work being done at the moment to simplify NM in various ways; all of which to in time become version 0.9. If you want to know more about the plans for NM 0.9, it's here: http://live.gnome.org/NetworkManager/ApiSimplify
When I'm connected I'm always happy to answer questions and help out in any way possible, both on NM and general desktop-ish stuff. You can reach me on #ubuntu-desktop or #nm on Freenode. I'm cyphermox.