I often quote different search representatives from what I find they say in the forums. One of the most quoted search reps is JohnMu, a previous webmaster turned Googler. I often quote him, then try to figure out any insight into the Google black box on what he said. I am sure he finds it funny, but hey - it is what I do.
In a recent Google Webmaster Help thread, John replied to a webmaster over links pointing to his web site from a spammy site. He was concerned it was or would lead to a penalty of some sorts.
Here is what JohnMu said:
In general, bad links like that to your site will not affect your site's crawling, indexing or ranking in Google's search results. Looking at those particular URLs, it seems -- at least for the ones that I checked which were still live -- that your site's URL is only used as text on those pages, the actual links are pointing to other pages. It's fairly common for spammers to use random text that they found on the web, so I wouldn't worry about this.
That said, if you should find actual links pointing to pages on your own site, then I would double-check to make sure that your site is not hacked. It's sadly also common for spammers to link to hacked pages.. but if you are certain that your pages are ok (if the cached version of those pages is correct, that's usually a good sign), I would not worry about that :)
So what do we learn from this?
(1) Generally, bad links pointing to your web site won't hurt you. A topic we discussed and debated here over and over again.
(2) Many spammers may include links to your site, but not activate those links, so you have less to worry about.
(3) Spammers often link to sites that are hacked.
Forum discussion at Google Webmaster Help.