In my experience, I know enough to get things done, up and running.  I know I'm not a 'true' DBA, but in a small environment, I can keep a database going.  But at heart, I'm a website developer and applications developer.

You know what is amazing though?  I get calls and emails from recruiters all the time, and they see extensive applications work on my resume, and where I list the DB's I've worked with (SAQL Server, Sybase & Oracle to name a few), the recruiters figure you're a DBA.  And then they try to sell me on being a DBA so they can land the contract.  I politely say I don't have the experience to be a true DBA, and I want a developers position.  Yet some get very agressive and tell me to think about it, or ask how we can 'tweek' my resume so I look more like a DBA.  I've even had a few who have said the position was a mix of DBA work and coding and when I get to the interview, I discover there's no development work, they want someone to be a full time DBA.  So sometimes, it's not just the candidate, the recruiters are also at fault.

And you are right, ProveIT and Brainbench show nothing more than your ability to take a test.  The most they can show is book knowledge.  Brainbench had a free weekend a few months back, take as many as you wanted for free over a weekend.  I took about 20 tests, I came to discover I was also a damn good sales & marketing person, I knew enough about the travel industry to be a travel agent and could also run a 4 star hotel!  Go figure!