My primary motivation in buying this year (like I really need much of a reason) is the upgrade to 32 GB of storage. What can I say? I like a lot of space. The CPU speed bump is nice, too. The device really does feel snappier in general. The 3G performance, however, is kind of disappointing (but in line with what I expected). Last year when I brought home my iPhone 3G on launch weekend, I was testing out at up to 1800 kbps transfers. Over the course of the year I observed performance gradually dropping until last week when I was lucky to see 500 to 800 kbps. With my new 3G S today I consistently saw 1000 - 1300 kbps again. I think it's going to be a constant battle between how many iPhones join the AT&T network and how fast they can add bandwidth.
I expect that next summer they should be releasing a 4G version. I'd really like to see a 64 GB storage option, too, but that might be pushing it. I'd settle for a multi-core CPU and real-world 4G speeds in the 3 to 5 mbps range. A new case design would also be welcomed. Sign me up.