a DBA is not a business per se (though it is an official filing of a business name you use), it's just a name YOU use to do business "as", hence DOING BUSINESS AS. A DBA (also known as a sole proprietorship) does not in any way to protect you, like an Inc, LLC or other form of Corporation may. I say "may", because you can not just set up a corporation and do whatever you want, thinking that you're personally 100% protected from your acts as a corporation.
As a DBA (or even an S-corp) ALL income the company makes, passes through to you, and it's considered personal income.. This presents some pros and cons.. If you're a C-Corp (typical corp), you may incur personal tax liabilities, as well as corporate ones, unless you have an accountant help you set it up appropriately to prevent double taxation - it's not too complicated..
A C-Corp is considered its' own entity, and is thus assigned an EIN (Employer Identification Number) which acts 'sort of" like a business social security number. I DO believe a DBA can be assigned an EIN as well, though, so check into that if you desire to remain a DBA.
If you have NO employees, and you're operating a business presenting little or no liabilities, and you're not worried about doing business with "big business" that may look at a DBA as unprofessional, amateurish or "small", you should stick with a DBA and get an EIN for each DBA you create (as a benefit for establishing adsense accounts using multiple EINs).
Essentially, you could create as many DBAs as you want..
Enough rambling, sorry if it's confusing, here's a great link explaining more about DBAs, how to file them, where, how soon etc..
http://www.mycorporation.com/dba/dbafaq.htm