ugh i read up on all this last year when i was searching on mods for the x360, don't rem a lot.
all the info is out there, do a quick google search.
there were two main production lines. the first had a faliure rate of something like 40 to 50% and the second was 70-80%. so hope that yours from the second.
besides that certain kernal versions turned out to be particularly faulty.
you should be able to tell everything from the serial number on the back of your xbox.
copied from another forum:
serial: LNNNNNNYWWFF
L represents which production line the Xbox 360 came from
NNNNNN (6 digits) represents the number of your Xbox 360 produced in that week
Y represents the year it was produced (5 = 2005, 6 = 2006, 7 = 2007, etc.)
WW represents the week it was produced (a WW of 01 means it was produced during the first week of the year). You can use this calendar to pinpoint the exact month.
FF represents the factory where it was assembled (05, 06 and 07 are all China based companies and are either Wistron, Flextronics of Celestica)