I just discovered this little gem by accident. I knit, and so I needed the actual physical size of my iBook, in order to create a laptop bag.
I opened Mactracker and attempted to highlight and copy the specs for my machine (from the General tab). However, when I clicked the specs, instead of highlighting, they switched to metric measurements. One more click seamlessly switched them back to imperial.
I exported the data, to see how that particular dataswitch was handled ... and, in the text version, the two are listed, one after the other.
It might not be a tip, but it was a nifty little feature(-ette) unknown to me, so I thought I'd share...
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060610043152128