The area of available bandwidth (avail-bw) estimation has attracted significant interest recently, with several estimation techniques and tools developed during the last 2-3 years. Unfortunately, some key issues regarding the avail-bw definition, estimation, and validation remain vague or misinterpreted. In this note, we first review the previous work in the area and classify the existing techniques in two classes: direct probing and iterative probing. We then identify ten misconceptions, in the form of fallacies or pitfalls, that we consider as most important. Some misconceptions relate to basic statistics, such as the impact of the population variance on the sample mean, the variability of the avail-bw in different time scales, and the effect of the probing duration. Other misconceptions relate to the queueing model underlying these estimation techniques. For instance, ignoring that traffic burstiness or the presence of multiple bottlenecks can cause significant underestimatio...