Does Lightroom 3 auto-update its database?
There is an auto-import feature, but it watches only 1 folder and no subfolders.
Practically, I don't rely on the Lightroom import function either, but I don't find the need to do a right-click/sync on a high enough folder a great annoyance (I usually update the "month" folder as I use a YYYY/MM/YYYMMDD structure).
Of course, YMMV depending on your workflow.
Lightroom should read all photo-capable bitmap formats.
I think Lightroom already does, as PNG is much more made for graphics than for photos (and TIFF/deflate does perform the same compression btw, if you really need this kind of things - TIFF/LZW is also very close).