With date-time picker I mean pop-up calendar.
I think that the annoying part is that while using 3 text boxes users have to click/tab on every text box - that makes 3 clicks/key presses. That's one of the reasons I don't like combo boxes.
But I think that you are write about the 3 text boxes. Users are used to this because of sites like yahoo and they will expect such interface in the other web sites they are visiting.
Validation will not be a problem while I'm using ASP.NET DateTime.Parse() method.
