Contrary to what others have reported I find the images to be way too big for web rendering. Even iPad 3 takes quite a bit of time to load fullpage pngs (about 1.5-2 MB for 1004 x 768 px photo) in HTML content. High quality jpgs are much much faster and should be provided as an option.
Another issue is retina support. Ideally, I would like to produce two versions of content – one std, one retina – to serve different content via Baker-like app depending on user's display resolution. It seems hard to achieve retina support now with in5. It should not be too hard to export images at 144 dpi and include them in CSS (or better yet create separate retina and std versions).