Trading Links? How Many Links Are Too Many? Time Frame?

I emailed a webmaster the other day asking him to trade links with me, and he replied that I should check back with him in a few weeks but he was full up on link exchanges right now. So I emailed him back asking if it was because my link directory was showing a PR of 0 in the Google Toolbar (it's a new site, and I wanted to explain to him that it was a high PR page, even though the PR hasn't updated on the toolbar yet.) He explained that he was trying to limit himself to about 10 0r 15 link swaps per month so as to avoid getting put into a penalty box by Google or one of the others for getting too many links too fast.

Bottom line is we're going to trade links in a few weeks.

But it was interesting to me, and I came across a post in the Link Development forum at Webmaster World asking whether or not excessive link-trading can cause penalties. This particular webmaster already has a certain number of link trades but was afraid that he might get kicked out of his positions if he had too many links. The general consensus was that there was no problem having lots of reciprocal links, but he needed to be careful not to get too many too fast, and he should try to get some one way links too, on top of his recip's. Good advice in the thread, and good reading. Slow and steady probably really does win the race at some point.