There is controversy surrounding this word. Traditionally a noob, unlike a newbie (who is simply a person new to the Internet or software or gaming for example), is someone who my be well versed in the online world but acts like a jerk. A n00b will spend time trying to flame others because they think they are above everyone and automatically know how to do everything. Noobs fail to see the fact that no one is a pro upon beginning an activity; you have to adjust to it. However, having said that, many gamers assert that the terms "noob" and "newb" are often used synonymously.
Even though pronounced the same, the terms "noob" and "newb" are, in fact, different. Popular belief maintains that being called a "noob" is truly one of the most derogatory names of all (so in an effort not to err, we recommend not making the mistake of calling a newb a noob ;-)