Despite the length of time it takes to get the Patent Office to issue a final decision in a reexamination proceeding, they are becoming more popular, as the charts below demonstrate.

Reexaminations are not appropriate in all situations because during reexamination the Patent Examiner will only consider printed publications and issued patents. What this means is that some of the best, most reliable evidence that could be used to demonstrate invalidity is unavailable, such as public use, knowledge, or the existence of an on-sale bar. Nevertheless, if you do have a publication or issued patent that demonstrates invalidity then reexamination may be the way to go because it is a far less expensive alternative to litigation, requests for reexamination are liberally granted and it opens another front in the fight to challenge a patent. Having said this, reexamination is hardly a panacea given that litigations are increasingly not being stayed and damage awards or settlements may need to be made prior to a final reexamination ruling, as was the case in the RIM v. NTP epic battle that ultimately had saw RIM pay more than $600 million to avoid the issuance of a permanent injunction despite continuing reexamination proceedings at the Patent Office.

http://ipwatchdog.com/2010/01/11/courts-reluctant-to-stay-patent-litigation-pending-reexam/id=8307/