Big, bright, high res -- choose any two
Seriously, I think your decision will depend on (a) whether you care more about size or brightness, and (b) whether you have at least some control over ambient light.
I jumped at getting a projector when the price for a 720p dropped to $1800 CDN and am *very* happy with the decision. At least two of my friends, however, went with large RPTVs because (a) they felt that brightness (and, to some extent, sharpness) was more important than the extra size, and (b) they were spending enough money that they wanted some future-proofing in the form of 1080p native resolution.
None of us have any regrets.
This is going to be a decision you really need to make based on your own priorities, and you're probably going to have to look at some systems to be sure. Remember that pretty much everything you see in the store is going to be cranked up to an insane brightness level and you probably won't want to run that at home, both for longevity and picture quality.
Finally, I'm not sure "projector now, TV later" is the ideal path... the same rationale that you use to choose a projector now will probably hold when it's time to upgrade.
I would be thinking either "720 projector now, 1080 projector later" or "hold off for a bit and get the 1080 TV I really want". Then again people say I think too much.