Ja no, putting together a business plan ain't fun, it's boring as hell. But, in retrospect, I think I should have done it way back in 2003, the year before iResign(ed) [this is the official taking the plunge phrase, endorsed indirectly by Apple, :-)]
I'd advise anybody who plans to 'quit and go at on their own' to put together a business plan first, it makes mundane things clearer. The market research is fun, especially when it supports what you want to do, ;-)
I hope it's the last time I do it (yeah right).