I've been coding in Processing for the last year, and I haven't bumped into any hard-and-fast walls limiting my options. It's pretty flexible, and the Java link magnifies options pretty extensively.
As blindfish says, there are some other options for different needs. If you learn Processing, however, you may find that this limitation may actually bootstrap you into other realms. For example, there's now an
Android port of Processing, there is a brand new
C port (for super-fast programs and iPhone apps), there's a
JavaScript port to control the browser directly, and ports to
Ruby and
Python. This means that if you someday need to do something beyond the core Processing capability, at least the code you wrote in Processing can link with projects and libraries in the broader open-source ecosystem.
