To me, the R9 290 is the trade-off card. On the one hand, you get similar, sometimes better performance than the stock GTX 780 for $100 less. On the other hand, you have a card that is loud, consumes a LOT of power, and gets super hot, could likely lead to thermal throttling, just like the R9 290X.
To me, having a card that sounds like a leaf blower and gets up to 95 Celsius is completely unacceptable, I don't care how fast it is. What I would do to correct this problem is to drop $75 and slap on an Arctic Accelero Xtreme III on it like Tom's Hardware did. So with that, the card's actual price is $475. With that, you have a cool, quiet, and now hopefully overclockable card that competes and sometimes beats the GTX 780 for $25 less. That's still a good value in my opinion. Here are the trade offs for getting the 290 w/ Xtreme III vs. 780:
Pros:
1. It's cooler and quieter thanks to the Xtreme III
2. It's $25 cheaper as stated earlier
3. It should be able to overclock now
4. It offers equal and often times better performance than the 780, especially at 1440p
5. Mantle with be huge if it doesn't turn out to be a fluke
Cons:
1. Not everybody wants to take apart a $400 GPU and put it back together
2. Disassembling the card voids the warranty, so if the card fails, you've just bought a $400 coaster
3. It still draws more power than the city of New York
So that's my opinion on the card. It's a great value, but it makes too many trade-offs to make me get all googly eyed about it. If AMD would get their heads out of their asses and let companies put aftermarket coolers on it, I would be getting googly eyed over it (idk why I suddenly feel the urge to say googly eyed).
In short, if you're willing to get your hands dirty, get the R9 290 with the Accelero Xtreme III.
If you want a card that performs well out of the box without getting hot and loud, get the 780.
I'm not claiming to be right, nor am I a fanboy, that's just my opinion.