IMO it probably won't. I wouldn't study for it if you have no intention of taking or using it.
I for example am not zend certified. I simply cannot justify driving so far just to write an exam I'm sure I'd probably near ace anyway :P
That said I'm also not a web developer, so I don't know. When I was looking for work out of school, no employer I interviewed with inquired about language certifications.
Oh, also its not mysql itself that's out of date, its the mysql library that is meant. The PDO and mysqli are newer libraries, but the mysql itself is still around. The library will disappear from PHP I'd expect for version 6.0.