themefinder.co
The previews are also responsive, so you can resize themes to see what they would look like on a smaller device (phone/tablet)
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...
Re result loading... yeah :( I have tried to improve this by 'buffering' the next theme in a hidden div, but it doesn't always work.
Actually, the loading screens are really just set on timers, so sometimes 5 seconds is too long, other times it's not long enough... I initially didn't have a loading screen on there at all, but it kind of ruined the user experience a bit if someone clicked the next button and the theme hadn't even started loading - they were basically just staring at an ugly grey screen with nothing happening.
Ultimately the problem with the current approach used on both my and the OP's site is that we're really at the mercy of the servers we're loading the demo themes off. Some are super quick, others are insanely slow. I think that I may have to do as you suggested and move to some kind of a screenshot / thumbnail first system.
For the speed issue; I was playing around with an idea of preloading the iframe previews to speedup loading; it worked but the browser would crash due to high CPU/memory usage eventually. Maybe you'll have better luck?
About the pre-loading, I'm actually already doing that... But only the next one in the queue. How many were you trying to load at once? I did notice that even only pre loading one is enough to slow it down considerably on my nexus 4 though...
BTW: I like your mobile/tablet previews. I was actually going to do the same but left it out for the moment :P
EDIT: Might be worth investigating the (dis)allow-scripts variable of the sandbox tag? Take a look at http://www.html5rocks.com/en/tutorials/security/sandboxed-if...
I actually came across it yesterday, dunno where I saw it tho.
Re seeing this on the front page sucking, not at all - just proof that great minds think alike :) But to be honest it did suck the way my initial submission seemed to disappear so quickly. Perhaps I just posted it at an inopportune time.
I'm not really in the market for themes, but maybe filtering by the of CSS preprocessor being used would be a nice thing to have? Also, the "checkboxes" do look like checkboxes but act like radio buttons, you might want to consider changing either the behavior or the look and feel. =)
Upvoted your HN original submission for what it's worth.
Then it keeps crashing safari. I tried multiple times but it always crashed either when first loading the page or when first pressing the arrow key.