I've used Tiles and Sitemesh for a number of years and while I personally prefer the Sitemesh style page decoration, I generally don't see a lot of mention of Sitemesh or Tiles on the Internet.
Do people use Tiles and/or Sitemesh actively, or are there other libraries that have taken over in this capacity?
I use sitemesh since it is less invasive than tiles. However I think that tiles is generally used in conjuction with structs 1.x?
We use Sitemesh, but I'm not a fan.
We use the apply-decorator feature almost exclusively, in order to wrap one of our standard page layouts around the unique content of each page. I believe this is better done with JSP tag files, because they are built-in to every container and are part of the JSP specification.
I haven't profiled it, but needlessly re-parsing all of the page content server-side in order to find the sitemesh tags and perform the re-writing has always bothered me too.