Just to underline a point about support here:
Someone will no doubt correct me if I'm wrong, but if you obtain your Plesk key direct from Parallels, you quality for free support when upgrading from a prior version. There's a special page for this which you'll find someone on the parallels website.
If you obtain your key from someone other than Parallels, you do not normally quality for free upgade support from Parallels - instead, you need to approach the third party you obtained your key from and they may or may not provide free support and support quality will vary.
This is perfectly reasonable: large hosting companies, for example, can obtain keys for much less than you'd pay Parallels direct, but the hosting company is expected to provide the end user with support.
As an individual, you can also purchase keys from third parties potentially for less than you'd pay Parallels direct. But again you need to approach that third party for initial support, not Parallels. Any support the third party provides may or may not be free and quality will vary.
And if you want, Parallels will support you no matter where you purchased/leased you key from, but for a fee.
The fee is not unreasonable, though I know that it doesn't fit all occasions. For example I've had a really small but annoying problem recently that I didn't feel merited paying that fee for. That's where these forums come in - there's usually someone who can help you, or at least get you on the right track. Not all the time - like we seem to be stuggling with this one, but usually. The Parallels KBs are also very useful.