Wow, just bought the software, nice stuff, I'll never ever regret my decision.. just what I wanted :)

However, I would have some ideas already:
- EXIF support for image captions, main parameters would be enough first, like: 90mm, f/2.8, 1/500, ISO100 (example for my 90mm Tamron macro lens)
- fix for Opera and Firefox, they don't play audio (IE: ok, Chrome: ok. Format: mp3, 128kbps, created by AVS Audio Converter)
- difficult zooming on mobile, at least on Android (HTC Desire HD). Image jumps away or next one loads when ending the tapping with 2 fingers.. (zooming in, Opera Mobile), image won't grow while zooming but the buttons do (default HTC browser). Not a big issue but needs some fine-tune I think

Please keep:
- embedding, flexibility
- nice quality downscale, no aliasing (originals are 1920x1280 and I don't let JuiceboxBuilder-Pro resize them, they come straight from PS in top quality - quality is retained even in non-fullscreen mode, cool)
- popup caption (just as others requested here as well) inclusive buttons, on mouse-over