I've been running the trial version of v.10 with no problems whatsoever.
In fact, I like it so much that I'm about to buy it as an upgrade from MovieStudio 10 Platinum (which has also been fantastic for the money!)
One question I'd like answered please:
I see that the build number that I'm running as a trial - and will be the one that stays on the PC after receiving the activation code - is 387.
If Sony updates the app, will they advise me, or do I have to keep checking?
Does it also mean that I have to remove the current version from the PC and download the newer one?
Thanks in anticipation...

If Sony updates the app, will they advise me, or do I have to keep checking?

You have to keep checking but I wouldn't worry about it as someone here always posts about updates.

Does it also mean that I have to remove the current version from the PC and download the newer one?

No removal necessary.
The update is the entire package and installs over top of the existing version.

Thanks Mike!

If Sony updates the app, will they advise me, or do I have to keep checking?

If "Use Net Notify to stay informed about Sony product updates" is turned on AND you're connected to the internet, you will receive a notification on your screen when starting Vegas if a new version has been released. It is on by default.

Thanks for the reminder Edward.
Most of the machines I use Vegas on aren't connected to the 'net so I always forget about that option.