QUOTE(warlord @ Jul 2 2007, 06:05 AM)

Simple, 3 years marriage based and 5 years work based GC's...
Not quite. It doesn't make any difference whatsoever how you got your Green Card (work based applicants sometimes marry USCs, and marriage based applicants sometimes separate or divorce). If you've been married to and living in valid marital union with a USC for three full years at the time of filing, you're eligible to file 90 days before the three year anniversary of gaining LPR status. You must remain married to and living in valid marital union with the USC until citizenship is granted if you take this route.
Otherwise, you can file 90 days before the five year anniversary of gaining LPR status.
Either way, there are other requirements which must also be met before filing, but often, the "continuous residence" requirement is the last one to be fulfilled, making it the one that determines when you can file.