Looking at the HD 5670 512MB reference card, this cements the fact that we're still too interested in cards with more memory than we really need to be. You can clearly see that the difference an extra 512MB of GDDR5 memory brings is really nothing. Unfortunately this isn't going to change the fact that we still want 1GB versions of cards that really only need 512MB.
If you're interested in saving some money, you shouldn't be worried about getting a 512MB version over a 1GB one with performance being almost identical between the two. In saying that, though, if you want to keep the temperatures down along with noise levels, it would be worth having a look at something that uses an aftermarket cooler.
Don't forget that if you go down that path, you'll probably end up with a dual slot card so if this is something you want to avoid, make sure you double check the cooler to see if it's dual or single slot or look at a card that uses the reference cooler.
Aimed for people who want to get EyeFinity on the cheap or simply want to do a bit of gaming at medium detail with resolutions of 1680 x 1050 or below, the HD 5670 continues to offer great value for money. While we would probably avoid the reference cooler, if a single slot option is a must it's not going to be the end of the world. Just know that we've already got companies out there offering better performing dual slot coolers.