upgrading 5.x to 6.1.5 or 7?

[Carl Brewer <carl%bl.echidna.id.au@localhost>]

G'day,
I'm planning to bump two amd64 virtual servers from 5.2 to 6.1.5 or 7 
tonight.

In the past, I've over-written the kernel with the new version, 
rebooted, then untar'ed the OS tarballs, over-writing everything, then 
run postinstall to tidy up /etc, and it's "just worked" - everything in 
pkgsrc kept working (cyrus, sendmail) and my home-made compiled stuff 
did too (mostly older Plone instances)

Any issues I might have doing that going from 5.2 to 6.1.5?  Or, is it 
safe to jump straight to 7 doing that?

the boxes are running as VMs so I will be snapshotting them beforehand, 
but I'm curious - any war stories?

thank you

Carl