I post some of my issues to Stack Overflow and other places on the web.
Should I be concerned about what people can deduce from these posts about my projects?
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What might concern you is that you are leaving a digital trace not only of your activities, but your ability to learn and ask effective questions. Thus, it's not not so much your projects which leak, but you.
If I interviewed you for a job, one of the things I like to chat about is the websites you use to keep current and seek assistance. If you mentioned Stack Overflow, that might be a rich source of additional information to make a hiring decision.
Based on your questions I know:
Which, to me, is rather generic and uninteresting. If you're really concerned about it, post "sensitive" questions as an anonymous user.
It only depends on you how much do you reveal. If you post much code, or a trend can be seen in your question, then some things can be deduced.
In my opinions you should be concerned about disclosing too much information. If your project is proprietary closed source, then your employer may not be happy about too much information flying publicly about it.
On the other hand, as statetd on the beginning, it depends only on you how much info you reveal.
This is debatable, I think you should mind your audience as much as your questions. If your project is sensitive try to recreate your problem in a similar situation without posting real code. This all depends on your company's policies.
If someone really wants to take the time to follow all of your posts on all sites, which is also possible in industrial espionage, there's nothing much that can be done unless you start asking your questions directly to a specialized support team where everything is kept from the public.
But then again the Internet is your best bet at getting help on pointy subjects. It's a risk to be taken.
Best of luck.