Oracle Spatial vs. PostgreSQL/PostGIS

[India]

I have a rather general question for this list-serv, which I hope is
appropriate, but would appeciate any input. I am a graduate student
researching the design and implementation of web-based decision support
tools. I am particularly interested in Open Source/Distributed GIS
development with Flash Interface design.

What are advatages/disadvantages from the Mapserver users perspective on
using the PostgreSQL/PostGIS database versus Oracle Spatial, aside from
the obvious expense of Oracle?