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Kiwiguy, I am very sorry to hear about the demise of your site. However, I still find it hard to understand how anyone would carry out a major upgrade on a production site, without first trialing the effects on a testsite duplicate.
It has been stated many times how important a duplicate testsite/backup is. It's easy to produce and ensures peace of mind during these times of upgrades hacks and trial changes.
We talk of 'stable releases' but in all honesty, the whole open source develoment scene is in a constant state of refining software and bug-fixing. Is anything 100% stable and guarenteed? Even today we see a new security issue emerging that affects previous 'so-called stable' releases. This is the nature of the beast. The software is all reletively new and there are bound to be problems that have not been seen or flagged.
To say the thing again.
If you have a valuable production site, make a backup that runs on your server, keep it closed to the public and use this to trial and test ALL upgrades, new modules, themes and hacks. Be sure the changes are not detrimental or can be fixed and THEN duplicate the process on your production site.