I prefer using springs under the pickup screws. You can get them at any hardware store.
Really the cleanest solution. If you tension the springs correctly you'll never have a problem. The "boing-boing" bassbenji mentioned really can happen, but is pretty easily cured by getting the right tension springs or adding some damping material (like, 'er a little foam) cures the problem and
gives you maximum adjustability.
The key is getting the pickups to the right height and holding them there without undue vibration. I personally love Alembic's system: There's one screw that pushes the pickup up and another that pushes it down -- end of story -- no vibration whatsoever. Not rocket science, nor (I suspect) a patented solution. Other builders could build this, but just don't want to add to their manufacturing cost.
This isn't an advertisement for Alembic, but only an illustration (for you Alembic-haters out there) of one of the numerous
design upgrades that go into the price of their basses.