I used Zaino's clay bar on my titanium silver 3er about 1 month after I had bought it, and honestly the results were negligible. Not a whole lot of dirt came off. Then again, I had already applied three coats of wax to it within the month prior, and that may have done a lot of what the clay bar would have, being that it was a brand new car and all. Another possibility is that the folks at Cutter BMW may have just detailed it so well prior to pickup that there wasn't anything to remove at all. 
Do I regret it? Not really. It wasn't that difficult, and now I have the peace of mind for the next year or so that I don't need to do it again.
Do I regret it? Not really. It wasn't that difficult, and now I have the peace of mind for the next year or so that I don't need to do it again.