After providing my email address for the ebook, I followed through and created a trial account for your site, and checked out the wireframing tool.
At first glance it looks nice, but I've been a happy subscriber to Balsamiq for over a year now and have no reason to leave at this point.
If there are any major advantages of UXPin over Balsamiq, it's not clear from a cursory look, which is all I have time for at the moment.
I'm also somewhat locked into Balsamiq, given that I have several ongoing projects there.
Hence, your 7-day trial probably won't be long enough to have any effect on people like me. Most likely I'll continue using Balsamiq for the foreseeable future, the trial will expire, and I'll forget about UXPin.
An alternative that might work better, would be to have a non-expiring free tier instead of the trial, with up to, say, 3 projects or something like that. Knowing that I can experiment with UXPin in my own time, when I'm ready (say the start of a new project which could be weeks or months away), and not lose my work, or not lose access to it in 7 days, would be more likely to tempt me to take the time to try it out, and ease into it if I find it better in ways worth making the transition for.
Hope that gives you a little insight into potential customers, good luck!