In this area, I wear my "web user" hat.
There are two ways I perceive "web spam": (i) when a good page gets contaminated with bad links, and (ii) when I do a web search and get a worthless page in the results. Both of these are forms of blight that make my life work.
Many forms of spammy link contribute to problem (i), whereas, as far as problem (ii) is concerned, I'm more concerned about the quality of the page than I am about the quality of the links.
Although some webmasters are "absentee landlords" and let people go crazy with XRumer on their forums, the majority of them hate type-I blight, and join with search engines to fight it.
Paid links, however, are a different matter, because, given the chance to get seven years worth of Adsense income in one lump sum (and still get the Adsense income in the future!), many webmasters will leap at the chance. If paid links are placed wisely, it's difficult to detect them and even harder to "prove" conclusively.
I think Google's war on paid links is unfortunately more about intimidation than it is about effective tactical action. I think some people will be dissuaded, but others will not.
The real problem that I see isn't the bad links, but it's the lack of good links. Many of my friends believe that 'if you build they will come' applies to web sites -- they learn the hard way that it doesn't. Maybe it was different 15 years ago, but organic links don't come easily in 2010.
"Quality" links are, definition, sites from people who have a lot more "juice" than you... Be that observable traffic or the elusive "Page Rank". There are what, 20 million web sites out there? Sure, most of them are a joke, but it starts getting tough to find sites "bigger than you" when you're in the top 200,000. You're still a "nobody" with a top-200,000 site, but you're still in the top 1%, so 99% of the sites out there aren't going to give you significant links.
I don't envy anybody who analyzes link graphs for a living, because the power law character of link graphs makes the data noisy and capricious. Link graphs are a powerful method for resource discovery for resources that are in richly linked parts of the graph (Wikipedia is a great resource... duh!) but linkage information doesn't give Google good information about the quality of "ordinary" web sites.