I'm currently finishing my ATPL theory. In Jan. '07 I have a financially-driven choice - pay for an instructor rating; or pay for a CPL.
If I go the former route, two local clubs get the benefit of an instructor next year that they wouldn't have. If I go the latter route I'll have a completely useless piece of paper for a year before I can afford the instructor rating.
Oh, and I won't be instructing for free. The clubs can charge a dual rate as usual - I simply won't be receiving any valuable consideration until CPL in '08. Clubs benefit to the tune of £25/hour for a year. I know CFI's at both clubs well - they know it's not in their or club interests to favour the 'free' instructor over those with CPL's.