i just got my 15" 1.5 GHz powerbook today, the machine is flawless; screen, backlit keyboard, build quality.
I purchased it using my educational discount and saved about 200 dollars.
I just upgraded from a 12" G3 600 ibook.
Already i can tell that this is going to be one of my favorite macs, after having owned 5 or 6 over the past 9 years.
My feeling is that you should be concerned about the display issues, but only mildly so, and also you should rest assured that apple will correct any problems that you might encounter.
I don't think these issues should prevent you from buying this machine for your son.
There will not be a powerbook update between now and August, the only advantage you might have in waiting is that there might be some added deals in a few months that some online retailers may add in that aren't available now.
hope this helps.