Slashdot | Comparing MySQL and PostgreSQL 2:

For an enterprise system,you also need:

1) Views
2) Triggers
3) Integrity Enforcement (i.e. if you try to insert 1000000 into a numeric(4,2) column of your enterprise accounting app you should get an error and not have something inserted).

As your system gets large you may also want:

1) Table partitioning
2) Functional Indexes, i.e. create index on table foo (md5(bar))
3) Partial indexes (i.e. create index on table foo (bar) where open IS TRUE)

MySQL hardly offers all of these capabilities.

PostgreSQL 8.1 will offer all of them in usable forms.

BTW, for those interested, my site has a whitepapers section [metatrontech.com] which has a MySQL to PostgreSQL migration guide.