How long does it take for a patent application to be processed?

Currently, the average patent application pendency is 24.6 months. Applications received in the U.S. Patent and Trademark Office are numbered in sequential order and the applicant will be informed within eight weeks of the application number and official filing date if filed in paper.  If filed electronically, the application number is available within minutes.

USPTO FAQ - Questions and Answers (14AUG2003)