The subject says it all. cmd-` on apple is the "goto previous document
function".
Product Version: NetBeans IDE Dev (Build 200807040101)
Java: 1.6.0_05; Java HotSpot(TM) 64-Bit Server VM 1.6.0_05-b13-52
System: Mac OS X version 10.5.4 running on x86_64; MacRoman; en_US (nb)
Userdir: /Users/hjs/.netbeans/6.5m1