We can discuss certification as much as we like but the problem is that you cannot generalize.
If you are sitting in a stable job and not intending to move soon - certification is not going to help much. You won't really learn anything relevant to your current job and the street cred that you have amongst your collegues is more important.
If you are looking for work, sometimes certification will help and sometimes not. If you find your next job by word of mouth, having a certificate won't neccessarily do much. If you are using job/cv boards where pimps (recruitment agents) trawl for buzzwords a certifcate may help you turn up in the search. Maybe 20% of the pimps use certification in their search criteria, maybe more - if you are prepared to ignore those 20% of the opportunities then skip the certification.
Some HR people use certification as a filter - not a good thing, but they don't actually have a clue and it helps them screen candidates. Again, you may not get your foot in the door because of buzzword screening.
If you are doing consulting assignments certification may help as part of the sales pitch. If you are uncertified and pitching against someone who is, the pointy-haired manager may choose the other guy.
I don't think certification helps much once you have reached the interview (or even the job) if the interviewer has done their work. As an employer I am keen on certs (though not all) because it demonstrates *something* - which differs from person to person and I establish the *something* in the interview.
For example if someone is sitting in front of me telling me how wonderful he/she is I ask "Why are you not certified?", to which I normally get some lame answer and ask,
"You say that you don't see any value in the certification? When did you last actually look at the content outline for (some) certification? What - never? So you don't actually know whether you are better or worse than the certified people, do you?".
This rattles them a bit and I finish off with "Well, if you are as good as you say you are, then you should be able to pass the exam with virtually no studying right? Okay, as part of your probation we'll pay for the exams but if you are not certified within one month of starting you're fired! How does that sound?"
The good ones are cool with it, the rest panic and start with excuses about not enough time 'cause their mother in law is sick and so on. Certifications and discussions about certifications are *really* useful in an interview situation.
Certification does have some value, it just differs from person to person and across situations. If I know a technology upwards, downwards and backwards then I don't see the *harm* in becoming certified.