I'm happy with Ubuntu 11.04 (classic no effects), and don't want to upgrade anymore to the more Unity and Compiz-centric 11.10 and beyond. Can it hurt me to stay at 11.04 for a year or two or more?
Ubuntu 11.04 is supported until October 2012. Until then, you will continue to receive stability and security updates. After that time though, support will be dropped, and if new security vulnerabilities are discovered, for example, you won't be covered. It's fine to stay with 11.04 during the duration of the support period, but after that you should start considering upgrading to a newer release, or switching distros / desktop environments if you can't learn to adjust to Unity or GNOME Shell by then.