Playlists for multiple takes
You probably all already know about this, but I only found out about it recently while perusing the mailing list on Nabble (which is another recent, and cool, discovery that I made), so here it is for any other newbs...
I've only been using Ardour for about 6 months and I must admit that I had trouble getting my head round the idea of playlists. I saw a topic on the list about doing multiple takes for a track and suddenly playlists not only make sense but it's a really useful feature.
When doing, say a guitar solo, or a vocal part, I used to just record loads of times into one track, layer upon layer. It was a pain having to re-arrange the layers to be able to listen to them all to find the best take.
Using the "p" button on a track in the editor you can create new playlists, rename them or select different ones to play. By recording each take in its own playlist you can quickly change which take you hear. I number the layers e.g. Solo 1.1, 1.2 etc and if I try doing something differently I might use different numbering, say from 2.1. Using the comments box from the mixer window can be really useful for adding notes ("this take is rubbish!" etc.) – it's just a shame you can't call up the comments from the editor window (I tend to leave it open and Alt+Tab between it and the editor).