I disagree with Mr Sukebe too. And I say that having just spent a lot of money upgrading to a full frame 5D2.
I see no prospect of full frame ever becoming cheaper or very popular. In fact I think it will become more niche and high-end. Most of the development money is going in just the opposite direction, into Micro 4/3rds format (smaller than crop format) and phone-cameras. As for competition in the full frame market, Sony pitched the excellent A900 against Canon/Nikon and seem to have got nowhere. Then they put out the cut-price A850, to a complete lack of applause. You can also get a used 5D now for very affordable money but it still remains niche. Full frame is the new medium format, and that never really caught on when set against 35mm film, even though the quality advanatge was very substantial - just too many other disadvantages, but mainly cost.
With crop format, I think the combined appeal of much lower cost and the long lens effective reach thing are very compelling arguments in favour of the crop format, plus a big weight advantage especially with long lenses. The point about less depth of field with full frame cuts both ways, and personally I generally prefer a bit more rather than less, but it's moot really.
I went for full frame because the quality is better. Not by much, and crop cameras are really superb these days, but full frame is better in terms of image quality if that is your number one priority. Always will be, even though the gap seems to be narrowing. That aspect aside, and of course it is a big one, I think full frame is nothing but a disadvantage. In selling my 40D and EF-S lenses, I've lost a lot of reach, which realistically I can only get back by hiring mega-expensive primes as and when. I've also lost the superb AF and fast frame rate that I could have got with a 7D body upgrade, and that would have saved me about £600. That's a lot on money just on a body, and of course lower down the range there are excellent crop format cameras for a fraction of the price of full frame - 50D and D90 for example.
Then there is the cost of selling stuff if you want to upgrade later. If you buy good quality kit, and you buy it well, you don't lose much. I was quite pleased with what I got for my 40D (that is really a brilliant used bargain these days - superb camera, with minters going for under £400) and especially my EF-S lenses - 10-22 and 17-55 2.8 that held their value very well. And whoever bought them will be able to sell them on again at pretty much what they paid me for them.