Oh believe me, I know! I mainly want to know now because how I plan this year's vacation time for work will depend on whether the concert(s) will be in September or October of 2011.
If I'm going to Ireland in October, I don't need to hoard my vacation time this year (we get new vacation days in October).
The best would be if it's right at the beginning of October, in which case I could probably bridge my trip between September and October and wouldn't have to withhold too much vacation time for the rest of the years!