My comments are similar to Dozer's comments. I think the easy answer is the X is whatever you can handle, comfortably or not, but there are a few questions that you should ask as well.

- What are the benefits to the day job? (HEALTH INSURANCE, 401K, did I mention health insurance?). Can you get these from a different source (family, spouse, etc.)
- Do your expenses vary greatly from month to month, or if they are fixed, are you satisfied with them being fixed and for how long (i.e., parents basement)?
- What is your earning potential over time with the day job or does this experience set you up for a better job (intern now, solid pay in a year...)
- Do you have other obligations that would need a steady income (Kids, wanting kids, whoops, your what??)?

I am a little older than most posters (35, ugh) so I have a different perspective, but to me, whenever I see this thread resurface on going pro I analogize going pro to jobs that pay on full commission like realtors or car salesmen. At first, a few sales give great income bursts and it is easy to take a few good months and project them over a few years for potential earnings, but as life goes on and the responsibilities increase (or you increase your spending to accomodate the temporary rush), more people move to steady income jobs because of the benefits and the certainty; it is hard to always live feast to famine and it can wear you out. Also, if you are smart enough to make a living playing cards, you are also likely smart enough to also make a lot of money doing something else.

All this being said though, if you are young, just out of school or looking to take a break, why not give it a try. Keep your business connections in place in the meantime and if it doesn't work out you can always go back. I just don't think you can go into it thinking you will retire a poker player.