Same problem, chrashes every time I switch from source view to design view.
Too bad, since design view is the only reason I'm trying out Flash Builder, for source view I stick to IntelliJ.
Well, found out that if I switch to Java 5, 32-bit, then Flash Builder don't chrash anymore.
Open Java Preferences, and drag "J2SE 5.0 32-bit" to the top under "Java Applications".
But, since Snow Leopard doesn't come with Java 5 (Java 5 is a symlink to 6), I guess you first have to follow the instructions to install Java 5 on Snow Leopard: http://wiki.oneswarm.org/index.php/OS_X_10.6_Snow_Leopard
If you want to change the VM for Flash Builder only, but not change it system-wide, you can edit the FlashBuilder.ini file (in FlashBuilder.app/Contents/MacOS/FlashBuilder.ini, or right-click FlashBuilder, "Show package contents"). This is equivalent to eclipse.ini in regular Eclipse installs. On the Eclipse wiki, you can read that you can add -vm
/System/Library/Frameworks/JavaVM.framework/Versions/1.5/Home/bin/java (before -vmargs) to select another Java VM. Or course, you need to install that older version first.
It seems to work for me...
I see this same problem on Vista 64 bit. I have 6 GB of memory but the error message always says that it is an out of memory error. I hope they fix this in the final release.
After making the changes to the vm in the .ini file, FlashBuilder won't even start. I can see the process start in the task manager, but then it just disappears but not error message is shown anywhere.
I believe Eclipse does not use all the memory that is available, but limits itself to the value set in eclipse.ini. If you change the -Xms and -Xmx options, you can increase the memory limit and try again. -Xmx is the maximum memory limit, it is set to 512m in my file, but try 1g or even more.