Dear protoDude,
I am not a lawyer, but did spend some time investigating this after I moved to the US from Belgium. First of all, it appears that state law determines whether or not non-compete clauses are even legal or enforceable. If you are currently living and working in California, for example, you most likely have nothing to worry about.
I have always found the following to be a the best approach in a situation such as this... During contract negotiations, provide a list of 'prior inventions' which are excluded from any non-compete agreement. In Europe this is standard practice, especially when contracting. Secondly, while under contract, and, when you are about to embark upon a new personal project, get sign-off from your manager that these efforts do not create a conflict of interest in your current role at the company.
There are multiple reasons for you to make sure that you dot the i's and cross the t's! You want to make sure that your employer is aware of the multitude of talents you exhibit and is aware of the products you are developing. And for you, it is imperative to make sure that whatever it is you are doing does not constitute a breach of contract. I believe that the benefits and hazards are obvious to this approach.
Finally, I would like to emphasize that your decision to contribute to the success of a company is not a one way street! When embarking upon contract negotiations or re-negotiations as described above, you need to make sure that you fully support your own decision to continuing to help your employer grow. If there is little to no support for the personal growth in which you are interested, you should terminate the contract and, if appropriate, find an employer who does support you as you support them.
Frank.