Cool -- I had no idea there was such a Google Fonts page.
One caution for those wanting to go font crazy: your ereader will be used for reading larger blocks of text, mainly. The classic text fonts -- mainly serif, some sans serif -- are classic because designers have fussed for a couple of hundred years over what works in terms of legibility and style. The past generation of typographers, working in the electronic / computer screen space, have refined these characteristics even further and produced a handful of very attractive and legible font face families.
The good news? The Kobo Touch offers a pretty nice selection of fonts very well suited to the device. You may well ache for an alternative (where is the palatino? the garamond? schoolbook century? futura? univers?) but at some point you'll want to get back to, erm, reading.
