To be honest; certifications have never made me get a job or a new client. But it sure helps your partner status for your compnay, as djeeg explains. The best way to show off your skills is well documented cases and references!
Currently the certifications are quite easy to get through, with a high score, even if you're not that experienced. One good thing though, is that questions on topics that you're not that familiar with will pop up - and if you're smart you digest that and learn those areas.
Having the certifications listed on your CV/LinkedIn account will also give you masses of recruiter e-mails :-)
Regarding the SharePoit Microsoft Certified Master, which is a 3 week training and a couple of exams/labs. That's a totally different deal. It costs you tons of money and gives you the best SharePoint training you can get. You can't expect to do the MCM with mediocre skills - you alerady need to be a really highly skilled dev/it-pro/architect. Unfortunatley - clients are currently not that aware of this certification. So consider it very carefully, so it's really worth it.