On a Monday I quit my job and gave my two week notice.
The next day my wife was fired.
The day after that, my old boss offered me a raise if I would stick around.
I did both jobs simultaneously for six months.
In my entire life nothing has been more lucrative than this. I've tried investing in stocks, bonds, and real estate. Nothing has been more lucrative than double-dipping.
The thing that's so bizarre, is that it also seemed to make me a better employee. I wasn't trying to be a scofflaw, I just kinda fell into it (due to my wife being fired). I found that things I learned from Job One made me better at Job Two, and vice versa.
I think a big part of the reason that this is, is because a lot of tech jobs are basically "human insurance policies." For instance, my employer paid me because I'm an expert in an obscure software program. So there weeks when I was busy as hell, but there were also weeks when I was basically there in case something broke.
I founded a forum on Reddit dedicated to this, it's called WWPGD. (A tip of the hat to Peter Gibbons from 'Office Space')