I am always a little concerned my boss will find one of my questions and think it was stupid or get mad at me for posting a question. Should I actively be sure to ambiguate it enough so he can't tell? I don't use my work email and clearly don't use my name as my profile name.
Most companies I've applied to, or worked for, asked me a very similar question during my interview; "If you're stuck with a problem, and your co-workers are engaged with something else, what would you do?" Here's a clue; the answer they're NOT looking for is, "Try to look busy until someone becomes available". I would highly doubt any manager would be angry at an employee for using the Internet to help with a problem. Heck, 90% of what I know about C# came from examples and information I found on the Internet, and the majority of that info came from this very site.
I wouldn't sweat trying to be stealth. if anything, that may come off looking worse. Just do what you do, get your job done and you'll have nothing to worry about.
First, I'm not a lawyer. Everything you get here is worth exactly what you paid for it: nothing. So take this with a grain of salt.
Stack Overflow gets hundreds of new questions every hour - check the new questions tab to see what I mean.
Because of this, any question you ask will be quickly pushed off the front page anyway, meaning that your boss would need to be actively looking for the question to find it.
Also, how would he identify it? I'm guessing your boss isn't a moderator, so he can't see your IP or email address anyway. And as long as you don't post identifying info (server IP's, identifying comments, etc.), there's no way to link a question to you.
Anyway, if I was your boss (I'm pretty sure I'm not), I would be perfectly fine with it. It's just education. If you're doing your job well, who cares what you need help with? I would rather my employees ask for help rather than just try things until they come up with something subpar that kinda works.
So you're fine :)
SO generally has fairly high standards of its questions. If you think that your boss would consider a question of low quality, it's probably not a good question for the site, and it's a sign that you should spend more time doing research, attempting to solve the problem yourself, etc.
If you get to the point of actually posting the question on SO it should be a question that you'd be proud to show your boss. Good questions demonstrate your skill as a developer.
If you have a boss that considers a fantastic question a bad thing for you to be doing, then you have much bigger problems.
If you use Stack Overflow at work (or on a company PC), you may be at risk - specifically from something like a key logger (although the probability that they'll actually be interested in checking up on that is rather low).
Or if you use your work e-mail, as you mentioned (but again, having a Stack Overflow profile is probably not going to raise any flags).
Other than that, and making an obvious connection between your Stack Overflow profile and you (e.g. putting your name in your 'About me'), I don't see a significant risk. And this assume both you and someone you work with are active enough on Stack Overflow on the same topics that they actually happen to come across your profile.
But you can also choose to go the other route - everything links to everything. Take the good with the bad. Some of your posts may be looked down on, but others may be good.