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I have Toast 10. I don't use it much, but I think it will be quite valuable, if only for the greater control over burning, and the disc cataloging application it comes bundled with.
 
I upgraded from Toast 7 to Toast 10 for better compatibility with Leopard, but that's about all. If you just want to burn CDs and DVDs, Disco is much the same and a lot cheaper.

Frankly, Roxio seems to simply be repeating the same bugs in Toast with new version numbers since Toast 4 and 5, so Toast 10 will probably be the last for me before I look elsewhere.
 
Usually a copy of Toast could last you a couple of years. The only reasons to upgrade really are if you need to burn on to newer media or for better compatibility with the OS.
 
I'm still happily using Toast 8 and see no reason to upgrade. Roxio seems like Intuit with Quicken coming out with an updated version each year to get your money with very little if any added functionality.
 
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