I don't recommend having a quantity as a goal. Quantity is irrelevant. Quality is key. Instead of loading up on weak links try to get links from on target web pages. Preferably with a good ranking for the terms you want to rank well for yourself. And of course if those pages have a high PR is doesn't hurt, either.
I guess we'll have to agree to disagree on a couple of points here. First of all, hard earned experience has taught me that quantity is extremely important, particularly if you're in a very competitive arena, provided that you have a targeted keyword phrase as the link text, and that your link is on a page that actually gets spidered by Google. Also remember to keep an eye on whether or not the link is actually a link that you'll get credit for in terms of it's structure. Some directories will require a recip and even though your link looks like a link at first glance, you may not get credit for it, and it gives them a one way link from you. If I see a directory that requires a recip, I usually just move on to the next one.
Second: The PR of a page linking to you has little to do with helping you rank higher. It has to do with maybe getting the little green bar to perhaps show another notch in the next update. Google no longer gives much, if any weight to what the PR of a page is that links to you in terms of actual rankings. They decided that it was much too easy to manipulate the PR. I would much rather have a few good one way links from PR 0 directories than a few links from higher PR pages that are either reciprocal or that have no targeted link text. IMO non-reciprocal links carry much more weight than recips, and are much easier to obtain. You have to remember that a spidered quality directory page is relevant to your topic.
I am in business to get my client's terms ranked as high as possible without going outside of Googles guidlines. Paying attention to what my client's PR is, or what the PR of a page linking to my client's site might be, is a waste of time and not productive in terms of my goals. I'm certainly not saying that you shouldn't do link trades, but IMO you should have at least an equal mix of recips to one way inbound links.