I haven't done any big projects with it, but I did use it for making a Firefox extension to archive sites. My biggest issue with it was the unpredictable way it would handle syntax errors, and how things were handled wasn't documented anywhere that I could find, you just kind of had to figure it out and remember for later. For example, depending on the function, passing the wrong number of arguments could 1). Cause the script to silently terminate 2).Cause the script to terminate with an error message 3).Execute the invalid function without mentioning the error, then return garbled output 4). Emit an error, skip the invalid function, but continue trying to execute the rest of the script.

It was frustrating enough to turn me off using languages that don't have compile time type checking.