well simply put lightrooom is like a super improved version of adobe bridge for handling batches of photos and improved version of elements tied together..
but if u do only a few photos and heavy photoshop
then lightroom doesn't work for it..
its more like a workflow solution ..
2. Simple enough to use as is
3. I started out with it and find no use to 'upgrade'
4. Good enough for my '1min PP' (ie. levels, curves, contrast, crop, B/W)
5. Add plug-ins (again free) and it really quite powerful
1. No good scissors tool (but then I don't want to spend too much time doing this anyway)
2. Less power layer (esp. no layer mask AFAIK)
3. Many tutorials will refer to Photoshop techniques, which will be hard/cannot be applied using Paint.net (main source of techniques will be fro mthe Paint.Net forums)