This is of particular interest to me because I'll be starting my full-time job hunt early next year (or even earlier because I get neurotic about these things), and I really only want to work somewhere that understands the appeal/necessity of "work where you want/when you want/on what you want".
How do I filter potential job opportunities on that criteria without being rude to anyone? I don't want anyone to think I turned them down because I thought I was too good for them or something, but the reality is that in a world where workplaces like GH exist, there's no reason to work somewhere that doesn't "get it" yet (and maybe never will).
Github is a very, very special company, and there aren't many companies out there that operate this way. Unless the organization as a whole adopts the philosophy you're looking for from the top down, this kind of freedom usually doesn't exist.
I think a good start is to begin early and search for companies that fit your criteria, then find ways to demonstrate why you would be a good employee to those companies directly. Don't go through the normal channels; find a way to stick out and be seen before you even apply.
Best bet: contribute a ton to a high-profile, well-known open source project that will stick out like a bright, shining beacon of light to your potential employers.
Filter based on if they're touting the work ethics you want. If they're not touting it from the tops of the hills, they probably don't do it. Places like GitHub and 37signals yell about how awesome their work environment is, if you want the places you're considering working at to be like GitHub or 37signals and these places aren't doing the same, I'd be wary.
If you're looking at bigger companies, find a list like Fortune's 100 best employers (for the US, sorry don't know other regions) and read it. There's a good chance what's written about the best employers is mostly true (not completely true, but it's a good guide). Also, ask other people who work for a place you're interviewing if you can buy them a beer / coffee the day after your interview. Pick their brain about the culture. If you're paying for the drinks and considering joining them, many people will be honest (I would be).
Don't feel you're being rude. I'd recommend telling the places that don't fit your desired culture exactly why you're not going to work for them. Worst it can do is nothing, at best, maybe the people who do work there see some tiny improvement.
I'm in a similar company at the moment - it's not quite GitHub, but the atmosphere of smart people working on things they love is there. Since I started they've also started adapting to the "Work when you want, where you want" approach as well ;)
When looking for work a big requirement was that I could work from home, and have Wednesdays off - filtering down the opportunities was just a case of mentioning that in the initial contact with a company I was interested in. No one you want to work for is going to be offended at you pointing out something that could be a problem early on in the process so long as you go about it politely.
How do I filter potential job opportunities on that criteria without being rude to anyone? I don't want anyone to think I turned them down because I thought I was too good for them or something, but the reality is that in a world where workplaces like GH exist, there's no reason to work somewhere that doesn't "get it" yet (and maybe never will).