Although it is often the only way to move a recalcitrant patent examiner, appealing claim rejections to the USPTO's Board of Patent Appeal and Interferences (the "Board") has its downsides, including cost and delay.   In a recent report, the Board reports that their average pendency has jumped by nearly 30% over the past year, and is expected to grow further.  

On a positive note, in addition to telling the patent examiner to pick a new path (which often is to allow the application to issue as a patent), those who win before the Board are also awarded with a Patent Term Adjustment to extend the term of the resulting patent by the amount of time spent waiting for the Board's decision.