Mac – Will upgrading the 2007 mac-mini from Tiger to Snow Leopard be a performance upgrade

For starters, OS X doesn't have the silly 64/32-bit dichotomy that Windows and Linux do. For most purposes, you can consider recent versions of OS X to be both 32- and 64-bit at the same time. The limiting factor in almost all cases of upgrading Mac RAM is the hardware chipset.

For your Mac mini 4,1: my copy of Mactracker says that the maximum RAM is 8GB. Your five-gig setup should work fine.

All of the press / industry coverage is focusing on the huge usability changes (and that mirrors the marketing that Apple is doing).

Some notable exceptions are the new Safari which runs some benchmarks like web app and JavaScript significantly faster.

The major changes under the hood speak more to security, sandboxing and plumbing the new multi-touch interface, encryption, auto save, auto revisions rather than speed.

It is too soon to tell if speed is much better, but once people adapt to the changes, the idea is we will be much more efficient with the computer waiting for us less than the other way around. I would expect your experience with the hardware you mentioned to be a minor speedup in pure numbers but a major speedup as your brain becomes free from worrying about saving, window management and revisions (assuming you adapt to the changes and like them)

I get the feeling that with mission control and full screen apps, that the UI is incredibly fluid and optimized but I'm running on some faster macs than yours.

Fun times, huh?