Please don't take this list as a list of requirements, that's not my intent, it's just what I'd prefer. And I'm not going to promise anything, I'm just wondering..
General stuff:
- Interested in contributions from other people (me), in code and preferably in design (up to a point ofcourse). (duh)
- Open Source (preferably OSI approved - for commercial stuff you'll have to pay me

- CVS and a Bug-tracker (or interested in setting one up)
- Mailing list would be nice, but... well... I guess web-forum will do too..
Technical stuff:
- x86 architecture, for that's what I know enough to develop on.
- C, C++ (or Lisp) will do, Forth might be possible, pure ASM no thank you.
- clean code written and commented in English
- general purpose multi-tasking desktop (preferably multi-user)
Ideology:
(here you can also give short reasons if you disagree)
- Microkernel, with our without drivers in kernel.
- Security as a goal, capability system would be nice...but...
- Simplicity is a good thing, as long as stuff is not TOO simple to work =)
- Usability as another goal, especially for power-users who like graphics

- I don't really care about POSIX layer, but it won't hurt and I can try to help with that too.
- Attitude to get something working "fast"..
- Interest in making the OS look nice - why code an OS if nobodys going to envy your desktop

Now, I'm not sure if anyone ever posted something like this here.. I'm not sure if I'm being too picky here.. but.. like... I need motivation to code, and I think best way to get that would be to co-operate with someone =)
I still repeat, I make no promises that I'll work on anything, but it sure sounds like a good idea right now. And like I said, nothing above is really a hard rule (except attitude for getting things done).