I use iRule, and while it sounds really cool on paper (err, html?), I usually go back to my harmony 650. That being said, it can be useful in some circumstances. Here's a tip: resist the urge to put every single button on your remote (direction pad, play, pause, seek, etc.) on the interface. Using a directional pad on a touchscreen will NEVER be as comfortable as using a physical directional pad on a remote. You do not want to have to look at your tablet/phone while attempting to navigate an interface on your TV. It's just a silly idea from the start.
I actually completely redid my iRule interface yesterday. It basically looks like this: the home page is an 'activities' page that let's you chose what you want to do (watch TV, play a DVD, etc.). From there, it launches you to a page that only has a few things on it. My 'watch TV' activity just brings you to a page that has a mute button (volume on the TV can be controlled from the tablet's physical volume buttons), a power off button, a back to activities button, and then a link to the Ceton companion app in the middle. Then I can view the channel guide from the Ceton companion app and select the show I want to watch. The Ceton companion app takes care of launching the show on my Xbox 360 extender. Notice that none of those actions require me to be looking at the TV while I do them. My XBMC activity page is similar. Instead of the Ceton app, it launches the Yatse XBMC app.