Sorry to hijack, but I literally just launched something very similar:
I even posted about it to HN the other day (https://news.ycombinator.com/item?id=7888745) but it seemed to vanish in about 30 seconds...
Now that I've got that shameless plug out of the way...
I really like the way you have executed on this - particularly the way you show each theme's description while you load the demo page in the background. Are you just pulling themes from ThemeForest at the moment? And may I ask how you're seeding your database? Are you grabbing RSS feeds, or have you built scrapers to go out and grab data from the various description pages?
EDIT: PS, can't get your blog link to work for some reason? I'm in Chrome...