Anyway it does seem like J would be a cool language to learn on. Oddly, they had a long discussion a few weeks ago on their mailing list about a good programming language for beginners (which can be found in their mailing list archive on the same site) -- threads like that don't usually end up with one clear answer, but there were a lot of good comments.
Here's a list of users from their website The following are a few of the corporate and academic institutions that use J: Cognos * Bayesian Enhanced Strategic Trading * Fax Focus, Inc. * Hewlett Packard * Intel * Korea Telecom * Luen Thai * Maple Partners * Microsoft * Niagara Mohawk Power * Nikko Securities * Novell * Okada Denki Co. Ltd. * Pivotal Technologies * SAP * Syngenesis, Inc.
Duke University * Harvard School of Public Health * Keio University * Lafayette College * Penn State University * Rochester Institute of Technology * Trinity University * University of Alberta * UCLA * University College of the Cariboo * (I wonder where the college of the Cariboo is, don't want to spoil my mental picture, which is full of reindeer, by looking it up...) University of Florida * University of Haifa * University of Houston * University of Iowa * University of Massachusetts (Amherst) * University of Wisconsin