Running for about two weeks now, I must say HHVM is very snappy. It can be rough around the edges while setting up depending on your system, but thats to be expected. I tried several installation methods, ultimately a manual build under Ubuntu 12.04 worked best. However I’m experiencing some issues with WordPress permalinks. Direct requests work as expected, but snappier.
I must say I’m most impressed by the performance increase via command line. We use several PHP based command line tools at DealerX. These tools comb millions of vehicles a week, cleaning and sanitizing and matching data for search and other end user displays. I think she’s a keeper.