I don't know how the OP wants to define "obsolete", but the Core i5/7 speeds are significantly faster than the C2D chips.
I personally would not want to buy a C2D machine but if I did not have a choice, then I could probably get used to the slower speed.
Aside from speed, the i5 and i7 aren't a whole lot different compared to the C2D. That's in terms of how capable the chips are (64-bit and all that). The Core Duo was obsolete simply because it did not support 64-bit, but otherwise the Core Duo was also about the same as the C2D speed-wise.
But I can understand that if given a choice, you wouldn't want to go C2D, and personally, I wouldn't either.
I stated how I meant it. There were a lot of rumors saying that Lion wasn't going to support core 2 duos, but when it released thankfully it did. So more than likely the next line of OSx won't. Which is what I'm afraid of. By the software stand point what I want to know is will I still be able to use this machine for the next few years without updating and upgrading issues as far as software? A couple have given their opinions based on such and I thank them
I think you were referring to Lion not supporting the Core Duo CPUs. And it did not, officially. Apple released the Core Duo (without 2) CPUs for a short while from 2006 to 2007, and then started using Core 2 Duo instead. Speed-wise, the Core 2 wasn't that big a step-up (not as big as the i5/i7 compared to current Core 2), but it supported 64-bit, and thus more memory in Macs that supported it.
For the next few years, I'd imagine that Apple would be hard at work at releasing 10.7.x updates instead of introducing 10.8 immediately. OSX is a workstation/desktop OS, and it doesn't undergo revolutions as fast as a mobile OS. Of course that's all just me.
Personally, I was in your boat. And I decided to suck it up and go Core i instead. The speed difference was something I very much needed, and it pretty much secured the update to Lion (no issue, no performance problem).
I wouldn't consider Core 2 obsolete just yet, but I can very much testify that Core 2 doesn't handle Lion that well at all.