A lot of people consider my 366Mhz iBook Clamshell w/ 128MB ram. Compared to my 17" 1.67Ghz Powerbook, I guess it is. But, it still does everything I need it to. It runs OS X, can connect to wireless networks, can run MS Office, and even Photoshop. This is an old computer, but it does it's job. I won't be buying any special software for it or anything, but I will use it for as long as it still runs. I will do the same with my Powerbook.
Sure, the current Macs will have lost some value after the Intel switch, but that will take a long time too. All Macs won't suddenly use Intel. And, Macs hold there value well. When can see a Powermac G3 in the newspaper for $300, it still amazes me. I could get a new PC for that. Maybe not a great one, but I could get one.
Developers are also most likely going to continue to develop for both chip platforms for a long time. There are simply too many PowerPC based macs out there to completely drop the platform.