Harris Geospatial released IDL 8.6 at some point in the last couple months—it's hard to pick an actual day. I've heard the release was rolled out to customers in batches since then and it was finally my turn last Friday!
The [release notes] list the new features. I am very interested in checking out the IDL Task Engine; I think it will be extremely useful. There are quite a few small features and changes that I think I will regularly use.
I will have more details in the coming weeks as I look at individual new features one by one.
[release notes]: http://www.harrisgeospatial.com/Support/ProductsUpdateDetails/TabId/1997/ArtMID/7326/ArticleID/14972/Whats-New-in-IDL-86.aspx "What's New in IDL 8.6"