One reason I made that decision is that my name is very common and I want something I can tell people that they have a chance of finding with Google.
Another is that if I release iOS apps, I'd rather have my brand on display in the store than my name.
Having a d/b/a also removes on potential trouble spot for companies who are concerned about contractor vs. employee issues with the IRS. Writing a check to Joe Smith is a potential audit red flag, a check to JS Design isn't. IMHO, this is more a perception of an issue than an actual issue, but when you're trying to get business it doesn't hurt to remove even perceived roadblocks.
I try to be very clear on my website that I'm a one-man shop. I don't want anyone to think I'm trying to look bigger than I am. I avoid writing "we," etc.