1) There are a variety of smaller sites that utilize reputation type systems. For examples, take a look at all those tech help sites (one called it exchange comes to mind). These all fit into the Question/Answer model. I think there is some merit to exploring blogging as a second option. Specifically blogs can use reputation threshholds for posting, filtering, and comment prioritizing (putting the good ones at the top). Basically those are the primary areas where I'd like to look to start building a user base, but I think there are many more out there.
2) As one commenter recommended, the service could be expanded to include more than just simple +/- karma type scores and move to more complex stuff like Kiva loanability etc. This is pretty self explanatory, add a service that makes life easier for these sites, and they'll ask their users to adopt it.
Finally, I realize openid is a different beast but it boils down to similar idea, universalize your identity. Login and passwords are, of course, prevalent everywhere, so there is a huge market for this type of service and it seems to be picking up some steam. Our target market is smaller, but if it proves nearly as useful to users within that space, it has a chance of being adopted as well.