I had that!
Ducati coventry said they could fix it but it would cost ££££££ so I left it because it was only a very small amount and was notgoing anywhere apart from in a little pool at the base of the cyclinder.
I think it only did it when the engine was really hot because I haven't noticed it during winter.
In my opinion, if you can afford it, fix it because it's better safe than sorry. Else wait until the next service.
Update: my was leaking from where the rear cyclinder tower met the main case, on the opposite side to the shock.
[Edited on 12-5-2006 by moozaad]