I am sure there are plenty of people currently working for small companies who think "I am doing most of the work around here, I should be doing this for myself". While that may be true, be sure to cover all of your bases prior to making the jump. There are several questions you should ask yourself.
Am I motivated enough to make the sacrifices needed to launch a company?
If you think you work hard now just go into business for yourself. You forget how much your current employer supports your efforts each day. Who will do the design, the development, the testing? Where will you work? Are you going to have a distibuted team or will everyone work from a single location. Will you allow people to work in your home or do you need a office? If you need an office consider renting an apartment or small offices in public storage facilities. These are great low cost solutions to needing a physical location. Who will do payroll, answer phones, write marketing material? How about accounting and taxes? There is a lot to consider prior to taking the plunge. Make a list and a plan. Write up a budget and do some calculations in Excel to determine when the cash runs out. It's not hard, you just need to put some thought into it.
How will you bank role the company?
This an important question if you will have some employees or contractors working on the project. There are a few options, your savings, family and friends and finally your network. Most likely these will be your only sources of capital. If cash is tight it may be better to delay the ship date of the product and continue developing it after hours. This will conserve cash and may just give you the time you need to succeed. Consider using college interns to help you finish out your product. Most will be extremely cheap and some will be free. Even though they are completely green I believe it is a better approach than outsourcing (those employees are probably just as green). Plus your can setup an office where you can guide the interns on a daily basis.
What market will you serve?
Are you going into the same vertical market that your current employer is serving? This should be a very big concern even if you are considering a totally different product from your employer's current offering. If you are you need to really consider what your employer may think. If your employer is a sole proprietor then you may want to discuss your plans with the owner. Even if you don't think you are infringing on his market space he may see it differently, especially if the owner is not reasonable. He may be crazy enough to believe he owns everything you've ever learned while employed at his business. You're probably wondering why this matters. Well it is simple, if he has more money than you then he can tie you up in court until all of your startup funds are spent plus some. Going into the same market space as your employer is effective sometimes and sometimes it is not. It really depends on the mental state/stability of the owner. Usually the bigger the business the safer you are. However you should tag it as a huge risk that you need to mitigate.
How am I going to sell my product?
You will have to devise a plan to market and sell your product. Is this sold via a direct mail campaign or through ad-words? Who is going to write your copy? What marketing gurus should you follow? Should you consider paying for individual marketing consultation with one of the gurus? Everyone knows the best product is not always the one that wins. Marketing plays a huge role in the success of a product. You should consider that writing effective copy may take just about the same amount of time as the product. Not each individual marketing piece but the refinement of the message as you prove the market strategy in the market place.
Who is going to support my clients?
If you are lucky enough to make it to product launch and sell a few then you have to support the product. If you are writing copy, fixing bugs, adding enhancements and gathering new requirements then how are you possbily going to have time to support the product. You could always just do forum based support but this might make your customers feel isolated. Just another concern to add to the business plan.
As you can see coding the product may be the easy part of launching the business. Most likely you have experience in writing software but the other areas may kill your business.