I just downloaded and installed iDesigner 5.0.1 for Mac OS X (iReport-5.0.1.dmg). But when I start it, nothing happens. Looking at the Console, I see:
2/18/13 11:47:00.572 AM com.apple.launchd.peruser.501: ([0x0-0x75c75c].Jaspersoft iReport Designer) Exited with code: 2
Not much detail, I'm afraid. My system is 10.8.2 (Mountain Lion) on a MacBook Pro w. 8GB RAM and about 100GB of free disk storage left. I have Java 7u13 installed.
Maybe useful, maybe not: I also downloaded the Netbeans plugin (4.7.1) and that works just fine.
I have the same problem. 10.8.3 (Mountain Lion). Java version "1.6.0_33"