If you run RubyMine using Java 1.6 after Java Update 4 RubyMine will not start. To fix it please :
1. delete *idea* file from /Applications/RubyMine 1.1.app/Contents/MacOS
2. then cp /System/Library/Frameworks/JavaVM.framework/Resources/MacOS/JavaApplicationStub64 to /Applications/RubyMine 1.1.app/Contents/MacOS/
3. rename *JavaApplicationStub64* to *idea* again.
4. add u+x permissions for *idea* file
By default RubyMine uses Java 1.5 and Java Update 4 will not affect it.
P.S: To run RubyMine with Java 1.6 you should
1. Change /Applications/RubyMine 1.1.app/Contents/Info.plist | Java | JVMVersion value from "1.5*" to "1.6*"
2. Increase /Applications/RubyMine 1.1.app/Contents/Info.plist | Java | VMOptions : --Xmx value because on MacOS java 1.6 is 64-bit and requires twice more memory than java 1.5
(info was taken from http://www.jetbrains.net/devnet/message/5237767#5237767 and http://www.jetbrains.net/devnet/message/5240216#5240216)
Update: We moved this faq to documents, see http://www.jetbrains.net/devnet/docs/DOC-1157