Pain, pain, pain
I tried Marcus's suggestion to no avail.
So, fundamentally, it can take many, many minutes for XP to boot on resume. But what I've noticed, using iStat Menus or Activity Monitor, is that memory acquisition by Parallels is an extremely slow crawl during this time--anywhere from 1 to 5 or so MB per second, or sometimes stopping completely at times, after an initial acquisition of 150 or so MB, with almost 1.4 GB RAM free. The VM is not responsive at this stage. It doesn't matter if the MBP has just been rebooted.
Watching this in real time it took 4 minutes to increase from 535 to 624 MB. (Of course, this is after already waiting for awhile to get to this stage from 150 MB). Then 2 more minutes to increase to 628. At this point, it doesn't seem to acquire more RAM until I click around the VM and attempt to start some apps, at which point things are quite sluggish but at least eventually responsive. So starting an app increased RAM to 815 within a couple of minutes, at which point no further increases at all are seen for another 3 minutes. Over the next minute RAM = 819, then stops, with no activity on my part. 822 after another minute. Went to dinner. Still only 843 in use. VM is usable at this point. During this entire time, XP Task Manager thinks it has the full 1024 MB.
This is in sharp contrast to how memory is acquired from a cold VM boot, where it essentially acquires all the memory, 1024 MB, within about half a minute after the XP boot splash screen disappears and locks it, and the VM works perfectly well.
Perhaps this memory management is all normally expected behavior after resume and has nothing to do with the performance problem at issue. I don't have a properly functioning mac running Parallels to compare.
In any event, it is orders of magnitude faster to cold boot than to suspend/resume. This has been going on for I don't know how many weeks or months. I just wish I didn't have to use Windows or Parallels at all.