Should I apply for a job with a future competitor to get some inside knowledge?

I’m a web developer/designer and had a business idea for a website about 10 years ago which, for various personal reasons have only started to take the time to start building over the last few months. I’ve had the site planned out for several years and done some design work, planning and research over the last couple of years. I currently have a full time job working as a web developer for a firm, I don’t have the funds to quit my job and focus on my own site for now. I’m spending time building the site in evenings and weekends and it’s now making good progress, especially since I stripped back a lot of ‘ideas’ after some reading of 37signals’ books and the lean startup.

Now, I'm not happy in my current job and have been keeping my eye on the market when the other day the company who I’d say would be my biggest competitor on launch of my own idea is looking for a web developer with exactly my skills and experience.

I’m wondering, should I apply? I’m thinking strategically it’d give me a great insight into how their site works and where they get their customers/contacts. On the flip side I don’t want to open myself up to them turning around and making out like I made off with their customer list or a copy of their code/database when I launch my site and they find out I'm behind it.

I consider that a lot of people must have worked for a company in the same industry before setting up on their own, potentially in competition, I imagine they’d also likely run off with a few customers too but would you say it would be unethical for me to apply or is it a great opportunity I should dive into and soak up as much information as I can?

Working for a company in the industry and working for a direct competitor are 2 very different things. The former provides you with industry expertise and the latter opens a can of worms by exposing you to a variety of protected trade secrets.

Most serious companies are serious about their intellectual property and make their employees sign a whole lot of various binding papers. These include non-disclosure agreements, original invention rights assignments, and non-compete agreements (some jurisdictions invalidate/prohibit these). As a result of these contracts, you will be sued if you go on to work for another competitor or setup your own company for anything from breach of contract to industrial espionage (theft of trade secrets).

A better course of action is to work for a potential customer (if your idea is for a B2B product). This way you will get the intimate industry knowledge that will allow you to create the perfect product.

Don't do it just for intelligence-gathering. There are so many thing that could go wrong with that, especially if your idea is pretty much the same as what they are currently doing.

Even if you get all their "plans" and all the insider knowledge, by the time you can execute on all that you will already be miles behind, as they will keep moving forward, iterating & expanding.

Not to mention all the problems you could get with working for them, from non-competes to IP theft...

On a side note, 10 years is a helluva long time to sit on an idea, is it something very tech intensive (aka. Big data or something like that) that requires a lot of funding, or is it something you can be lean about, build a minimal version and test it out?