I've been looking at switching to a password manager like that, but I've been having trouble knowing how to pick one that a) I can trust and b) is good. I was thinking of giving up and just using a plain text file inside a truecrypt file.
LastPass fit all these, but it might not fit your usage requirements. However, I would urge you to investigate it and all other options (KeePass seems popular, as are some other Firefox extensions) if you don't currently have a good password solution, as any of these is better than using the same password multiple places.
Advantages? I guess I should try out LastPass. Free or $1/month premium is a good price.