Tweeting before you have seen/heard the product is an issue, but you can at least customise the message when you "pay" - e.g., "About to check out the new Band X download. See what you think: http..."

Stumbled across Pay With A Tweet in the wild a couple of weeks ago and thought it was quite novel. That said, I didn't know that it let you customise the message and didn't really know the band I was checking out, so I didn't make use of it.