Just deployed a Citrix Netscaler Platinum into our SoftLayer infrastructure.
While we are quite confident in Domino and XPages security, a recent application vulnerability scan highlighted a couple of areas where Domino comes up a little short.
I have been evaluating the Netscaler for a few weeks and pretty much it's a web application administrator control freak's wet dream. Our primary purpose is to put a web application firewall in front of our application to add another layer of security but the other benefits such as enhanced caching and SSL offloading are also very exciting. (Side note: Even though we'll use the Netscaler to process client-facing SSL, we'll likely continue the SSL behind the Netscaler for the backend network to do our part in trying to thwart the, shall we say, "overeager" in our government.)
Over the course of a year these things cost as much as pretty decent used car but, just like when you get a new car, you don't care about the price when you see all of the powerful functionality at your fingertips from one of these bad boys!