There is a lot of confusion about what web 2.0 sites are but I will assume you are talking about websites like Squidoo, Tumblr etc.
If this is the case, the best software I've used is Senuke. It's best if you take the time and learn how to post multiple times with the same accounts.
I'm sure there are other tools that can do the same (MS or UD) but I've played most with Senuke.