Precision and range (so, everything important ;-p)
From MSDN:
The DateTime value type represents dates and times with values ranging from 12:00:00 midnight, January 1, 0001 Anno Domini (Common Era) through 11:59:59 P.M., December 31, 9999 A.D. (C.E.)
Time values are measured in 100-nanosecond units called ticks, and a particular date is the number of ticks since 12:00 midnight, January 1, 0001 A.D. (C.E.) in the GregorianCalendar calenda
Date Range: January 1, 1753, through December 31, 9999
Accuracy: Rounded to increments of .000, .003, or .007 seconds