Actually, I've been looking into smart antennas too lately.
To my understanding, they are used in addition to Rake fingers, in order to enhance multipath diversity - meaning to receive multipath component of a certain signal and add them all together to increase the SIR of that signal.
Smart antennas, restricted to just a discussion on actual physical antenna is nothing more then beam selection or beam steering. First level created several years ago with cellular tower was a triangle shaped antenna that separated the pattern into three 120 degree patterns. The directionality gave more gain and interference rejection allowing more call carrying capacity per cell tower.
Newer antennas can electronically steer the beam to focus on a needed direction or steer a null to reduce interference. Multiple antenna feeds with independent steering can be accomplished with tight control over amplifier gain and phase tolerance feeding splitters that can then individual phase shift paths and combine with other antenna elements path to accomplish fine adjustment on beam directionality and nulls. Since this part of the smart antennas involves much of the receiver electronics path (DSP), the definition of smart antenna must be expanded to encompass a whole reception system.
It is like your brain figuring out what direction a sound is coming from by sensing the amplitude and phase difference from your two ears.