And also a HUGE improvement in a lot of different areas! Speed, especially.

I'd just never gotten around to it... Nothing I used (except Kod and new Smultron) really required 10.6.

It is much buggier, frequent crashes of Safari, iTunes and Mail for instance

Not sure why you are getting down-voted. I have 2 MBPs. One is s ~3 year old running 10.5 and his baby sister running 10.6.

This is entirely subjective per my experience:

- the 10.5 'feels' more responsive.

- the beachball is a very frequent event in the 10.6, specially Safari, sometimes even when switching tabs which is quite annoying.

- I haven't rebooted the old MBP in months. Sitting pretty on my desk. The new one has frozen few times and occasionally I feel the need to put it out of its misery myself.

There's no such thing as a trivial OS upgrade, and so long as 10.5 is supported and runs the stuff I need to run, I don't have a compelling reason to go to the trouble of upgrading.

You'll have to excuse me, but you're wrong. I mean, sure, it is an OS upgrade. But there's no real "trouble" (it takes about 20 minutes and a few clicks) and there's definitely compelling reasons to upgrade (including running 10.6 specific software). One pressing reason to upgrade: 64bit. Another one: cocoa finder. Also, faster and smaller.

Seriously, I know people who have a reason not to upgrade. You don't seem to be one of those people. Those people are on worse operating systems than you are.

OK, tell you what: you come over to my place, run the upgrade, then fix all my dev stuff (combination of macports and non-macports) that'll break. Seriously, I've done this before and I know what's gonna be involved. But if you want to sit back and tell me how little "trouble" I'll have, you can do it for me.

... except some software that's 10.6 only? ;)