The current mono garbage collection is sub-standard and requires work around for any title considering console style gameplay. All instantiates and destroys are accompanied by unacceptably large GC spikes (in web and stand-alone)
I tested the Unity military demo on 3.0 in the profiler to verify that this has not been addressed.
The sgen-gc option generally has far superior results. http://www.schrankmonster.de/2010/09/01/taking-the-new-and-shiny-mono-simple-generational-garbage-collector-mono-sgen-for-a-walk/
While there are time-consuming memory pool work arounds, not all of them are available from script without working around large swathes of audio and effects code (And of course the unshippable OnGui)
Unity could really compete against other PC engines with reliable frame rate from scripts, so I can't encourage this feature strongly enough