Ah, the joys of getting frustrated because what worked one moment doesn't work the next... and then you remember you jumped databases:
Oracle : The core system
MySql: Message Boards and Private use
PostgreSQL: Caching System
Sql Server: Crystal Report, Analysis, .Net apps
MSAccess: The quick hacks in
VB - i.e. batch insert into lots of other databases from Excel
This runs a bit like our programming languages:
TCL: The core system
VB: Batch jobs
ASP: Dynamic content and streaming apps
ASP .Net: Internal apps
Java: Replacing the legacy TCL
It's hell... I would heartily recommend any organisation to reduce the tools to a manageable lot rather than go for the 'best tool for the job' vs cost effectiveness type management... you just end up with proliferating environments at a higher maintenance cost.