Phil Ringnalda and Ian Hickson are thinking about extending HTML with search engine hinting tags.
I totally agree with this, as I mentioned before. The questions are whether the attribute should be on a block or on individual links, whether we should have more general link typing or simply "vote abstain" ("vote against" is a bad idea), and whether Google could handle it.
For authors, the most useful seems to have an "unendorsed" or "nofollow" tag for blocks. Supporting that tag on a link level is definitely lower priority.
For Google, I would expect that a tag on the link would be easier to handle, parsing-wise. I really wish the Google people would chime in on this.
I was also glad to hear that finer level indexing hints actually exist and implemented in some search engines (FDSE), but again Google doesn't not seem to have responded to these suggestions.
Update: Some indications that Google is making a move.