Valid? Yes, if it is an option.
The smart (experienced) surfer sign up for 5-6 trial sites instead of one monthly membership, grab all content, and sign up again for trials months later to grab the updates.
I think the best solution on this "problem" would be something like this, let say with a 3 day trial: Assume you have X GB of content, you can make a daily/hourly bandwidth limit on the trials so they can't grab it all.
Just make sure its in your terms
Or make something like "Silver/Gold" accounts, with limited access, only preview.
However if the paysite is bad, it wont help at all.
