UPSC has just released the Examination schedule for the year 2010. If you are still wondering when the UPSC CS (Main) exam will start, the answer is 29 October 2010 and will last for 21 days. Of course, this is subject to change as written in the disclaimer (which is very rare). See the snapshot below saved from the UPSC website few moments ago.
It also has the dates for other UPSC exams such as the CDS, NDA, IES, Geologists’ exam, Central Police Forces Exam, Indian Forest services etc.