I remember a site clinic several years back featuring taiwan email list a Google's webspam chief, Matt Cutts. He was reviewing a site's link profile on stage using an internal tool and commented that while Google saw several hundred links to the site, only three (yes 3 out of hundreds!) were passing link equity. Cearly, the search giant does a tremendous amount of filtering on the web's link graph, so don't presume to be sure which links are passing value.

I recommend taking the low-risk road. In the long run, they're likely to get penalized/devalued and you're likely to overtake them with a link profile that's clean and continually increasing in value. Where do you draw the line between money that's spent to acquire a link indirectly (as with event sponsorship, ads that turn into links, etc.) This gets at the crux of the issue, but I think I've got a reasonably good methodology for determining which links requiring funds fit with Google's guidelines and which violate them.