Here's a fascinating one.  This is as simplified as I could get it.

1) Create a presentation using PowerPoint (I have PowerPoint 2002), in ppt
format.   
2) Make a slide with the Title Only or Title and Text format (not Title Slide).  
3) Add centered text to the slide title.
4) If you print the presentation from PowerPoint now, all is well.  Save and close.
5) Open the file with OOo.  Save with Save As and close.
6) Open the file in PowerPoint again.  Looks fine on the screen.
7) Print the file from PowerPoint, and notice that the centered text shows up
left-justified.  

I originally saw this with a large presentation that looked fine on screen but
all the slide titles were mangled when I printed.  I can only reproduce this by
creating the file with PowerPoint first and importing in OOo.  Note that I did
my testing by printing to a dummy PostScript device, but I also saw this problem
when printing to the fax modem.

While the bad behavior is occurring in PowerPoint, I suspect that OOo is
generating data in the ppt file that PowerPoint doesn't know how to handle.