ooh, I have so many questions on this topic
1. Spike has his soul back - does he feel incredible remorse for what he has done and feel some need to repent for his previous sins (far too Angel for it to be a possiblility)? Or might his remorse turn him completely mad, having to deal with the guilt might send him over the edge?
2. Even if he does have his soul back, doesn't nessecarily mean that he's going to be a good person. His soul will act as a conscience, but doesn't mean he's nessecarily going to listen to it. And if this season of Buffy has taught us anything, it's that having a soul doesn't stop you from committing wrong.
3. Could the whole thing be a scam - I mean the demon might not have given him a soul at all and just be waiting to see how he's going to react, thinking that he has a soul?
4. Like Highlander said, the soul might not be a human one or the way that we understand it. Might mean he is re-demonised after all.
5. What's happening with the chip?
6. Will he retreat to being William or stay Spike?
7. Did he even ask for the soul in the first place?
8. What's going to happen when Buffy finds out?
I dunno - too many questions and far too long to wait to find out the answers.