According to my current experiences at a somewhat large tech company certifications are not essential to becoming a PM.
What evidence is out there to support the decision to either get certified as a PM or skip the certification process?
My general opinion about certificates (completely subjective):
Certificates increase the possibility to get into a certain position at a large company. HR representatives are looking for these certificates and if you have them, you may be able skip certain questions during the interview process. You can even get the position if the interviewer accepts the certificate as an indication that you master certain skills or at least you know about them. Large companies love the certificates.
Certificates won't help you stay in a certain position even in a large company. The theoretical knowledge you gained while getting the certificate won't help you stay in your position, unless you are well connected. The thing is to be good at what you are doing - no matter what the role is - you need the skills to apply the theoretical knowledge in practice. And this is what you learn on the job.
Small companies doesn't care about your certificates. Small companies are very choosy when it comes to hiring, and they want to see what you know and not what others think you know (certification).
I've been interviewing candidates at different companies for a while now and we have never accepted anybody just because he or she had a certification. We checked what the certification is about and validated that the candidate really knew what it is about and not just went there and got some papers. In my experience, companies are looking for practical knowledge and care less about certificates.
The last one: they are expensive and takes a lot of time to be certified.
Here is my advice for you:
Don't go for a certification. Find a mentor instead, who let's you to stay close to him/her and let's you to learn how to be good at what you would like to do. If you still want a certification after this learning period, it will be much more easier with some practical knowledge behind you. This is what I did when I wanted to be a good ScrumMaster.
I don't know a truly canonical answer for this, as I have not researched it exhaustively. However, salary and market surveys can provide some factual answers, although you certainly have to discount for bias--especially bias based on who sponsored a given survey.
For example, here's one data point:
This survey says that a Project Management Professional (PMP) typically earns 12% more than an uncertified counterpart, and that a Certified ScrumMaster (CSM) generally earns 6% more than a PMP. However, survey methodology, selection bias, and regional or industry variance are not broken out, so you should not take the stated results as anything more than a starting point for your own research.
Certification might make you more marketable, and possibly give you some additional domain knowledge, but it certainly won't make you any smarter or any more talented than your natural abilities provide. There are many talented PMs without certifications, and many certified PMs who can quote book-and-verse but flounder in real-world scenarios.
Whether or not a PM certification has value to you will depend entirely on how valuable you find it in the marketplace. Technical and PM certifications have always had extremely marginal value for me, and I tend to discount them heavily when I'm in the interviewer's chair, but your mileage will definitely vary.
Knowledge, ability, and experience are more valuable than certification on the job, but education and certification are often used as proxies for measuring those things. With that in mind, having a few letters after your name rarely hurts, and it can be a great tie-breaker if all other things are equal when a gatekeeper is sifting the resume slush-pile.
At the end of the day, the decision to pursue and maintain one of the certifications is personal. There is no legal restriction or prohibition from practicing project management without one. But more and more hiring managers are using a certificate as a hiring filter, either a firm requirement or a heavily weighted one. In the public sector in the U.S., it is becoming a requirement to lead projects and tasks.
By May of 2010, there were a little less than 390,000 PMP practitioners. The rate of growth is impressive.
There is no empirical evidence that suggests certified practitioners out perform non certified practitioners. I found one study, a doctoral dissertation, that hypothesized a difference, and it showed that PMPs were more apt to deploy more formal processes--especially risk management--in terms of documented proof; however, found no evidence that suggested overall better performance.
The Pros of pursuing it are: 1) it keeps you in the mode of learning, 2) it will help you bypass HR filters. The cons are: 1) it is reasonably expensive, 2) no evidence that you will improve your PM skills.
Anecdotally, I have observed no difference in knowledge or performance. I enjoyed personally studying for it myself but I have no idea if it made me a better PM or not. Around me, I have not witnessed better performance and have chosen to remove it as a filter for hiring...unless it is a requirement for my client.
In theory, someone who has passed an exam (example: PMI) knows a minimum of the Project Management Body of Knowledge. In reality, I've interviewed people with PMI certification who knew very little. For some HR managers, it's still one benchmark they put up as a minimum requirement. Very few people confuse this with being a real manager.
Becoming a good PM requires a lot more:
Understanding project specific risk
This non-exhaustive list is above and beyond all the formal techniques (which are still important). The best way to learn this is to find a great PM and work under them.
Many certifications require some portion of continual education and/or involvement in a project management community outside of your organization. This creates an opportunity to learn material outside of your company and to hear points of view that are outside of your working world. This kind of diversity and education can be a benefit at companies that value innovation or out-of-the-box thinking/new ideas.
Bottom line: it depends on the culture and nature of your company.