So, if you're actually trying the "ignorance is bliss" strategy for managing $dayjob relation, then consulting a lawyer up front could save you an awful lot of trouble later.
As for those types of contracts assigning tech IP to $dayjob, that’s what I was alluding to. If you have one of those, unfortunately you cannot start a business without risking $dayjob wanting a piece (or all of it). Regardless of how often they stand up in court or are even tentatively enforced, I wouldn’t want to risk it.
I know this depends on the company, but, as a general rule, are these clauses really taken so lightly?
I fought the good fight against some silly assertions such as "They could not have built this in so little time without overlapping working hours" but lost the battle when the VCs pointed to the timestamps of some support/feedback comments posted by one of my Engineers on the project's website. He had written those and posted during working hours while sitting in the office of said "day job"
Project squashed, all the IP was rolled up and shelved. It was a bad day.
TL;DR these clauses are typically not enforced because your side project is typically viewed as worthless. If on the other hand your project is seen as a source of value... tread carefully.
In short, by taking these clauses lightly, you are creating failure paths for yourself that begin from the initial light of success. You may not want to kill your big success even before it happens. If your goal is just to create a side income, you would most likely be fine simply because a lawsuit would cost more money than what it may recover, or you may just get some threats/scoldings.
I have heard that if your side project or startup reaches something like $10 million in revenues, your big-company employer actually becomes liable to their shareholders to recover this money from you since it technically belongs to the shareholders.
Some high-profile entrepreneurs have told me that you should not worry about lawsuits as they only come when you succeed and when you do, you have resources to take care of them. But I have also known specific cases of things doing down because of such issues (like the example from etsimm, who also responded to your comment).
By the way, YCombinator submission form includes a question on such IP issues, though I may guess everyone just blindly picks "No issues" for it.
> What does your boss/supervisor think of your startup?
My boss had no reason to know, although she eventually found out through other means. It didn't affect my day job at all so it was a non-issue. I had no reason to bring it up and neither did she.
> How much do you talk about it at work?
Not at all. Work is for work.
> Are you worried that your full-time employer will think you're doing your work on their time?
They knew me well enough to know that I would never do that to them.
> Are you worried that you may be technically doing your work on their computers (even by logging into Asana or a similar site)?
Do not do anything on work hardware, ever. In many parts of the US this may actually entitle them to something (though IANAL and don't want to open that can of worms). Just don't do it. There's no reason to.
Ideally, you wouldn't even do startup-related things on your personal hardware (e.g. phone) during work hours or while at work.
> How do you juggle meeting clients, contacts, mentors, other cofounders, with your day job?
The job I had when I was doing this had an owner who was a butts-in-the-office type (part of why I left). Because of this, the simple answer was "I didn't," unless it was over lunch. If the folks your meeting with know you're working full-time - they probably should - then they'll know you can't meet for coffee at 10 AM. Most of the time they will be impressed that you respect your employer enough not to use their time to build your business.
The job I have now is not so stringent on time. I could go have coffee with someone at 10 AM if I had a really good reason (up to me to decide), and we all put in enough hours that nobody is counting how long you're away from the desk.
> How do you send urgent emails related to your startup in your day job?
As I said earlier, work is for work. It needs to be really bad to require attention from you when you're being paid by your employer to do what they want.
I obviously can't answer the last point, but I'd like to leave you with one thought. It would be great if everyone had the time, ability, and means to bootstrap a business on the side while getting paid full time, but the unfortunate truth is that some people don't. You may have a job that required you to sign something prohibiting it explicitly. You may just have a job that is too close to your passion such that any business would be a competitor. Or, you may just have an asshole boss who makes you work 60-80 hours a week for a 2% raise and a $300 Christmas bonus.