Receptional_Andy - 8:19 pm on Jul 9, 2008 (gmt 0)

I've not seen any direct connection between ranking and sitelinks (blocked or otherwise) although sitelinks do give a good overview of how Google understands site structure. I would suggest that sitelinks are an effect, rather than a cause: site problems (especially structural or hierarchical ones) can be made more visible via sitelinks, but I don't think sitelinks themselves have any potential to cause ranking problems.

I would expect the impact of removing a sitelink on ranking to be nothing, aside from whatever changes occur to clickthrough rate as a result of the missing link or whatever replaced it.