Although there's no more development on CyanogenMod 9 any more, the occasional nightly is still appearing for the HP TouchPad, presumably when the main CM9 code gets a security or bug fix that triggers a rebuild. I'm keeping an eye on CyanogenMod 10 for the TouchPad too of course, but it's actually my Nexus 7 that I decided to jump to CM10 first on.
The three most useful features to me that CM10 provided over the stock Nexus 7 ROM were using a launcher that rotates the home screen to landscape, the ability to overclock from the Settings (rather than having to install a third-party app to do that) and the simple addition of a battery remaining percentage to the left of the battery icon on the status bar (saving me having to install a third-party widget to get that crucial figure that really should be visible on all Android devices, IMHO).
Oh and don't forget to install the Amazon Appstore app on your TouchPad and other Android devices to get the Free App Of The Day. I hate the Amazon Appstore in so many ways (slow to load the page of apps, have to tie credit/debit card even for free purchases, confirmation e-mail sent even for free downloads, massively smaller store than Google Play), but the free app of the day makes it just about bearable to keep it on your device. I can't find a UK free app RSS feed or UK free app notifier yet which would make it easier to remember to go each day to get the free app.