I think it depends on lots of different things. Until you've done work in, say web backend programming, you probably shouldn't persue a non-entry level job doing that task. The same goes for the various disciplines that are out there.

On the other hand, once you've shown that you can tackle pretty much whatever's thrown your way, then the walls between different tasks tend to disappear, and you become an experienced "senior" type guy.

On yet another wavelenght, jumping in with both feet and being willing to be "under water" for a while is generally a very good way to learn any task.

-Scott