Before i started clickjoy.com which has been successfully launched, I started on a great idea and got 2 co-founders , everything was exciting , i could feel the chi flowing. Even talked to angels, invested some of my own money into outsourcing the UI look and feel. However soon the symptoms showed, my cofounders had to take their kid to the hospital, travel here and there, wife got sick, too much work, scared of layoffs, this weekend,next weekend, definitely wednesday etc etc. I was the only one working hard and after 2 months of excuses, neither of them did *anything* i mean literally - not even accessing the machines when i monitored the logs.
So finally i called quits. i still believe in the idea and maybe someday i shall find the resources to pursue it but for now i just made a practical decision instead of an emotional one.
not sure what your story is but my advise is not to cut too much slack when dealing with a cofounder, give a few deadlines and if they dont meet any in weeks or a month , simply let them go.
* on a side note this is why NEVER ever register the company with a cofounder's signature before the probation period- else you are looking for a nice law suit when you do succeed eventually. Also suggest atleast asking them to email you a disclaimer for your records so they cant claim you stole their ideas.*