Back in my dot-com days, when LifeMinders was flush with cash and everybody was still throwing money at us, I asked that in lieu of an annual raise, I keep the same pay and shift to a 32-hour week, Tuesday-Friday. And they went along with it! (That ends up being something akin to a 20% pay raise if you look at the hourly rate rather than the annual salary, so I was worried they'd balk at that -- but I think after the 50-60 hour weeks I'd been working the year before, they kinda felt they owed it to me.)
I managed to arrange a 4-day work week one other time in my life, for which I had willingly taken something like a $450/mo pay cut. It lasted for three glorious months and then both laurie_robey's and my car both died abruptly ... and the new car payment for Bruce ended up being exactly $450. So back to work for me. :P
If we weren't skating on the edge of "just getting ahead of our finances" and I could afford the pay cut, I'd take it in a shot to get back to the 4-day work week I loved so much. All I require of my day job is that it pay the bills and stay out of the way of my Real Work; having Mondays to dedicate to that Real Work, so I can spend the weekend giving due attention to familial obligations, chores, and actually doing some relaxing, enables me to get a lot more done.
I was unfortunately somewhat mired in depression for some of those Useful Mondays, and I also had a tendency to expect too much of them -- like getting angry if I didn't get a whole week's worth of strips drawn in one day. But there were also plenty of times that I spent the whole day writing or drawing and finally felt like I was actually putting my life to the purpose for which it was intended ... which is a great feeling. :)
Of course, shortly thereafter, I had a whole friggin' year off from work, which turned out to be more of a curse than a blessing ... but that's for another ramble.