I'm still trying to get an idea of how much the memory speed can affect normal use. I'm not a gamer at all. I use a lot of memory using CAD software, running microsoft's visual studio (shouldn't be as hardware intensive as it is), converting many video formats, and simply using commercial software, like macromedia flash, photoshop, and other products like that. Generally, I like to multi-task.It's still not worth it. The prices have come down, but even if DDR3 was fast enough to actually justify the cost (which I don't think is the case), you won't need all the speed - you don't even need all the bandwidth of piss-cheap DDR2 in single-channel.
I read an article on Tom's Hardware whatever testing out two identical systems, only difference being that one used dual-channel, one single-channel memory. The difference in games was only a few FPS in favor of dual-channel, and the improvement was only marginal in all other applications, meaning that as long as you have your DDR2 in dual-channel, it'll provide enough bandwidth for a while.
No reason to go DDR3, yet.
And of course, DDR2 is the cheapest way to go
Would I be better off going with more low end memory, or less, but of a higher quality/speed? I'm building a new system, and am trying to build it around my habit of multitasking, I've found a good motherboard that supports DDR3, but there is a nearly (if not, I'll have to look back) identical version of it that supports DDR2.