Four reasons I won't upgrade to Leopard:
1. The dock
3-D? No thanks, I need the screen real estate
2. Stacks
Honestly, I only have a gist of what this is, but from what I've seen it's not something I'd like.
3. The new finder interface
Do we really need this? I've heard so many complaints about it, it's not worth it.
last, and definitely not least least
4. Resources
Even if I wanted Leopard (which I don't), I simply couldn't do it with the hard drive space I have and the amount of RAM I have.