Yes, this. I consulted with a business attorney in Silicon Valley on this particular issue when I was considering getting a startup going on my own after hours

Yes, this. I consulted with a business attorney in Silicon Valley on this particular issue when I was considering getting a startup going on my own after hours. She basically said that there is enough "gray zone" in what I wanted to do vs. what I was doing for my employer (although I felt they were really distinct areas of computer science) that if my former employer wanted to go after me they could easily bury me in legal BS. Whoever can spend the most on lawyers wins...