MAX233 -- capacitor between power and ground

I bought a MAX233 for an RS-232 interface, partly because it didn't need "external caps" and so I thought it'd be easier to wire up. But the "typical operating circuit" shown in the datasheet shows a single 1 microfarad cap (granted, this is a smaller number than most of the alternatives use) between pin 7 (Vcc) and ground. I have a few questions about this:

  1. What does it do?
  2. Is it necessary?
  3. How important is the actual value? I don't have a 1 microfarad cap handy.

Thanks, all!

Excellent! Thanks; guess it's off to Radio Shack then.