Google has put out a new Webmaster Help video about how many links you should have on a page.
In summary, Google used to advise people not to have more than a hundred links on a page, but now you can get by with more than that. According to Cutts there's no real limit, though there might be. Just don't have too many. But don't worry about it too much.
Confused? That's because there's no real answer here. The basic gist is just: be reasonable. Of course that's subjective, but here's what Cutts says:
He says, "It used to be the case that Googlebot and our indexing system would truncate at 100 or 101K, and anything beyond that wouldn't get indexed, and what we did, was we said, 'Okay, if the page is 101K, 100K, then, you know, it's reasonable to expect roughly one link per kilobyte, and therefore, something like 100 links on a page.' So that was in our technical guidelines, and we said, you know, 'This is what we recommend,' and a lot of people assumed that if they had 102 links or something like that then we would view it as spam, and take action, but that was just kind of a rough guideline."
"Nonetheless, the web changes," he continues. "It evolves. In particular, webpages have gotten a lot bigger. There's more rich media, and so it's not all that uncommon to have aggregators or various things that might have a lot more links, so we removed that guideline, and we basically just now say, 'Keep it to a reasonable number,' which I think is pretty good guidance. There may be a limit on the file size that we have now, but it's much larger, and at the same time, the number of links that we can process on a page is much larger."
"A couple factors to bear in mind," he notes. "When you have PageRank, the amount of PageRank that flows through the outlinks is divided by the number of total outlinks, so if you have, you know, 100 links, you'll divide your PageRank by 100. If you have 1,000 links, you'll divide your PageRank by 1,000. So if you have a huge amount of links, the amount of PageRank that's flowing out on each individual link can become very, very small. So the other thing is it can start to annoy users, or it can start to look spammy if you have tons and tons and tons of links, so we are willing to take action on the webspam side if we see so many links that it looks really, really spammy."
If you're concerned about having too many links on a page, Cutts suggests getting a "regular user," and testing it out with them to see if they think it has too many links.
So, in the end, just ask a friend, "Hey man, do you think this page has too many links?"