Thanks for both helpful replies!
My site is Technologyexchangelab.org, a nonprofit site that collects technology that's particularly useful in mitigating problems of poverty and sustainability around the world. It's a custom-made (not by me) site built on MySQL, PHP5 and jQuery, The heart of it is a growing database of useful technical solutions, categorized in ways that make it easily searchable. We also host a growing number of articles, and lists of other resources. We would like to implement a CMS to better manage these things, although we are not looking at replacing the solutions database at this time.
If we could somehow 'embed' processwire into our existing site and use it to manage our articles and lists of resources, that would be a major improvement.
I looked into using Drupal, Joomla and Concrete5, but was incredibly put off by the complexity, intricacy, eccentricity and steep learning curves of Drupal and Joomla, and the dreadful slowness of some rather small sites (smaller than our own) using Concrete5. I was particularly put off by how much you have to "just know" about how each one goes about things, ie, that if you add or change something here you must also make a change there, or it simply won't work right. I spent one long night trying to create a simple article entry process in Drupal, basically enter or paste text and upload a picture, and it just plain wouldn't work right no matter what I did, and if it had worked right, what other things would I have to suffer through just to get it to post these articles to our web site as embedded content w/o having to port the whole dang site into Drupal (or Joomla)... yuck.
The point on Perch is well taken. If we got it doing exactly what we wanted, who's to say that sometime in the near future a request to extend functionality might leave us trying to get Perch to do something it wasn't designed for. So, if I knew that we'd never need more than Perch, that's what we'd use, but since we don't know that, I think processwire looks like the better and most easily implemented solution for us.