I enjoyed your podcast about the book possibilities in AP2.1 and ironically, I had only an hour or so earlier posted a comment on Apertureprofessionals about a problem with custom fonts selection. I thought it might be worth posting here too.
There is one aspect, when trying to customise a book layout, that is hugely frustrating. Custom font changes CANNOT be applied to Master pages, well ... they can but they don't 'stick' when you subsequently apply the Master to a child page
So yes you can change a font on a master page, for example, if you add a 'Metadata Box'. However, if you then apply that Master to a Child page, the font reverts to the default font in the Template. Very frustrating. I'd almost call it a bug. If you have the ear of Mr Schorr, please pass this one along.
I discovered this limitation a few weeks ago when I was printing 100 50x60 prints from a Z3100. Aperture prints really really well and the Book tools were a great way to handle the job (not least because the job now sits in my Aperture library and can be revisited at any time). These were fine art prints and Apple have perhaps not really considered the possibilities of using Aperture as a batch/archive tool for fine art printing, but it turns out that it's really good at it. But this 'bug' was really a pain. As I worked my layout and text, back and forth as is typical for me, I had to manually alter the font in 100 child pages because the default fonts replaced my custom choice.
Another thing that would be great, is to have the option to turn off the whole book metaphor thing and just see a load of prints. It would help too if images weren't always offset to allow for the gutter ... because it you're printing to an inkjet, you don't need a gutter.