After running EqualLogic for a couple of years now, I have never experienced any real issues with the boxes. Running what seems to be a customized version of NetBSD they have proven to be fast, and reliable systems.
I was performing what is now a routine Firmware update from version 5.1.1 to 5.1.2, I have already done this on a PS6000 we have setup for Replication with no issue what so ever, and left upgrading our production Array untill I was happy that the Replication Array was working fine with the new firmware. Satisfied I decided to update our production PS6000 to FW 5.1.2. During the upgrade I recieved a Kernel Panic and subsequent Panic Recovery, looks like the controller crashed during the update this resulted in the iSCSI targets being unavailable for a couple of minutes, the controllers did not fail over and I now have a Firmware mismatch.