Ahah! space bar does work for pagedown, I'm just used to using the page down key *g* I really miss the home key, though.

Command tab is fine between apps, but tabbing within a form on a webpage is what I miss - for example, once I've finished typing this comment ordinarily I would just hit tab, which selects the "post comment" button, then hit enter. But on the MB, pressing tab now takes me to the search box text field at the top of the page.