I just bought a GTX 680 and don't feel terribly threatened or deflated by the imminent release of the "685". The 680 is a significant upgrade from my 470 and couldn't be happier with it. Thing is there are many folks who asume the "685" will somehow be released as a direct replacement and at the same price as the 680 (which would leave me feeling ripped off) but bear in mind it is already going to cost some £150+ for a 4 GB 680 so I suspect the "685" is going to be fairly pricey. Unless you are gaming over 1920 res or running a multi-monitor setup the 680 is an excellent performer for the cost.
There is always going to be something bigger and better around the corner and for me at least it's all about buying the best hardware within my budget at the time and the 680 has delivered. I got this mainly because I currently require a card with a minimum of Compute capability 2.1 and as a bonus it runs all of my games at max settings smoothly ... without having the presence of a jet engine. Arguably the 580 has better compute performance according to early benchmarks but some of the new features that were introduced with the 600 series tempted me.
In short, I think I'm going to be enjoying this card for some time regardless of what appears next.
Well said, as long as you are happy with your card or cards and they do what you need of them. Then there is no reason to upgrade or chase the latest and greatest.