I have an iPhone 3G and happy wiht this. I'm not sure why "everybody" want's the new iPhone 4, beacuse the 3G can do almost everything like the 4.
The iPhone 4 has of course more CPU, more RAM and a better display, but that's becuse it is a newer model though.
If you do the right things you can have an iPhone 3G that can have folders in the iOS, use multitasking (i can manage to have up to 6 apps running at the same time) and have a video recorder for the cam.
The downside with the 3G is the low amount of RAM. It can be a bit slow sometimes, and you need to have a watch on your memory status. The positive side though, is that the iPhone 3G now is very cheap :D And that's good enough for me!
I will tell you more about how to get this to work, but if you want to have all this opportunities you must jailbreak your phone. It's a simple operation, and if the correct instruction is followed it's completly safe.
I will make a guide for this, but new software is made all the tiome so it's not so easy. But it will come.