Thomas Thurman has posted short but excellent tutorials on how to develop apps for the Nokia N900.
On Part 1 of Thomas’ tutorial, he shows how to create a client for the social bookmarking site reddit. He provides the links to references and downloads, which are quite handy for first-time developers.
On Part 2, Thomas talks about packaging. He also adds an icon to his Raeddit app, and then shows a screencast on how it looks so far.
I hope he keeps creating tutorials as it looks like more and more newer developers would look at developing for the N900 and Maemo 5 soon.
EDIT: added Part 2.
This is good. It would be even good, if the SDK can be installed in native Windows. I read that people are working on that. So, waiting for that first!