The automatic links to booksellers provided with ISBN numbers are a good feature overall.
I'd rather have them not point at Amazon, though, since they are obviously against freedom (keyword: 1-click patent), and didn't respect my privacy (details on request). I would be more comfortable with links to other outfits (Barns & Noble, whatever).
Obviously you may differ on this issue, and if the links to Amazon are kept, I suggest that they use the Amazon Honor System. With this Bomis would receive payment for every traffic that reaches Amazon through one of those links (just like with banner ads). AFAIK, the only thing that must be changed is the base URL used in those links (e.g. putting /wikipedia/ somewhere in there), and of course registering with Amazon. If you implement this, please put up some page stating where the money goes. I'd expect Bomis to earmark the money for the hosting & maintaining costs of wikipedia, but it's always good to have an explicit statement.
Perhaps other booksellers offer similar deals, or they could be worked out individually.
What do others think?