I think digital cameras, at least the GOOD digital cameras are actually holding their value longer and longer as time goes on. During the great megapixel wars, yes, a 4mp camera became obsolete as soon as the 6mp's came out... and they went out the door when the 8mp's came out and so on. But I think anyone with half a brain realizes that past about 12mp the return on gaining a mega pixel or two is getting more and more negligible. Look at the Epson Rd1... it's ANCIENT in "electronics years" but there's still many people still using them and many who would pay a premium to get one.
Yes, there will always be a better camera around the corner, but as a photographic tool the Nex 3 for example will be a good option as long as it still powers on. I just picked one up last week, and after reading all these threads about the next gen Nex on the horizon I realized I now longer get that sense of dread and disapointment I used to get when I heard a new version of my current gear is coming out. The Nex 3 does what I want it to do and I while I'm sure there will be bells and whistles on a new version I'll envy, I won't be chucking my Nex 3 at release date of it's successor.
Same thing happenned with my Canon 50D. I had the 30D before it and, when the 40D came out I said no big deal. when the 50D came out it was a definite step up and did things image wise my 50D couldn't do. Now there's been the 7D and the 60D and neither would change the quality of my photos. Yes, bells and whistles and a few more MP's but nothing that would make me concider my 50D obsolete.
So I skipped one generation between my 30D and 50D and it's been arguably two generations now since that and I haven't felt I'm working with obsolete equipment. Unless technology radically changes I think we've reached somewhat of a plateau in digital camera technology where all they're going to be offering us is more bells and whistles. As usefull photographic tools, i think our cameras are actually increasing in lifespan... not bad 🙂