The New York Times has a blog entry in Gadgetwise about designing a logo. The advice appears to be sound except for the following item:
SCOPE OUT THE COMPETITION
This is important for at least two reasons. One, you don’t want to be on the receiving end of a trademark suit. (You should also trademark your logo.) And two, you want your logo to be distinguishable from those of similar businesses. Your logo should be exactly that: yours. Of course, some companies choose to piggyback off the success of their competitors by creating similar logos, but it’s better to branch off. You should not, however, shy away from adopting elements you like. Just make yours better.
Chances are if you talk to your trademark attorney and tell him or her that you want to trademark your logo, you’ll have to endure a brief lecture about how the word “trademark” is not a verb. The lawy
er doesn’t do this to be a scold or to sound officious, but does it to help explain what exactly a trademark is. A trademark or a service mark is a word, a graphic or a symbol that identifies the source of a product or service as separate from other sources. A product has trademark protection once that product is delivered or used in the marketplace and consumers associate a identifying mark with that product. It’s the use of a logo that confers trademark status, not the legal registration process. For example, if you’re starting a sneaker company and you decide to put three vertical stripes on the sneakers to 
identify them as coming from your company and not Converse, the logo is not a trademark until the shoes are sold and customers recognize the stripes on the shoes as coming from Adidas. Registering the logo, either at the state level or federally, provides additional enforcement benefits, but the registration alone doesn’t make the logo a trademark. That’s why a logo or other mark may have the symbol ™ for unregistered trademarks or ® for registered trademarks. Neither confer trademark status, but the trademark symbols are notification that the logo is a trademark.
So if you want to skip the lecture, ask your lawyer instead if the logo can function as a trademark, whether it’s federally registerable, or if it’s available.