Thought I'd add to this topic since I'm about to go through a divorce, and I-751 waiver scenario, and just met with an attorney on the subject.
Basically, you have to be divorced before you can file I-751. INS don't keep track of marriage records, so unless your ex-wife calls INS and rats you out, they won't know that you're out of status.
My suggestion is that during the time it takes to get a divorce, gather as much joint evidence as you can. In some cases, best to do this before asking the mrs for a divorce in case she goes crazy and destroys everything!
As soon as your divorce is finalized, your conditional GC is not longer valid. I still have a year to go on my Cond. PR, but was advised that it's better to get divorced now, rather than wait until close to the 90 day < 2yr anniversary of getting GC to do it.
One you've filed an I-751, you can still live and work in the US while INS are making their decision. They might approve it without an interview, if there's enough evidence and they're happy.
I was originally here on H1B and still had 2yrs remaining on it at the time I got my Cond. GC. Seems like that's going to help me prove that the marriage was bona fide... I had no reason to get married to stay here seen as my visa was valid for a couple years. Had my H1B been expiring real soon at the time of getting married, that wouldn't look too good.