I've been using harvester as well after you mentioned it in a tweet.
Well pleased with it for time tracking, but I'm afraid I'm still mucking about with document templates for my invoices. (although I do use harvester to calculate everything, just don't use the generated pdf)
But that's because it's not in the format which is standard for the netherlands. Although they have said in the forums that more customizable invoices will be a feature in the future.
None the less, makes keeping track of hours much easier!