The thing about abstract logos is that they seem fairly easy to create, so many amateur logo designers come up with abstract logos for their clients and the logo just does not float. Probably the most common mistake that inexperienced logo designers make is creating an abstract logo that is too generic. In other words, an abstract logo that started as a circle and never really progressed beyond a circle. Sure it has a nice gradient fill and a shadow, but it needs to be more. It needs to make the jump from being a generic shape to being a shape that is unique to the company it represents.
With this in mind it would not be a stretch to say that abstract logos are possibly one of the more difficult types of logos that logo designers can tackle. There are after all only so many things that you can do with a circle, right? Well, no, there are in fact limitless things you can do with a circle to make it into a great abstract logo, but it requires both a creative mind and a bucketload of real-world design experience. If you have your mind set on an abstract logo, you would do well to look at your logo designer's portfolio first. If you are not convinced that your chosen designer or design firm has years of experience, don't hesitate to move on. There are many more designers where she came from! Or save yourself the headache and get your abstract logo from LogoAnts! :-D
For further reading on abstract logos:
Definition of abstract logos according to the Logo Design Dictionary.