As with all Ubuntu distros, support will eventually come to an end. In the case of Ubuntu 11.04, the end is nigh, with just over a month left until Canonical officially pulls the plug. Natty Narwhal will go down in Linux history as the first Ubuntu to use Unity as the main interface.
The upgrade path is fairly straightforward – you won’t be able to do a leap directly to 12.04, but you can do so incrementally via 11.10. Canonical have some very thorough instructions on how to do this if you are unsure. Even if you’re particularly fond of 11.04, it’s well worth updating, with more desktop choices if you dislike Unity, and a better version of Unity if you do.
The end of life also coincides with the impending release of Ubuntu 12.10 Quantal Quetzal, the post LTS release by Canonical.