I use Hootsuite to post to all of these networks and help schedule my tweets. Or if I blog or have a photo, I use posterous and it updates my networks upon post. What are you looking to do?
Each network is a little different so not all content is repurposable - directly cut and pasted - on each. I'm sure the other community members can share what content they use for each and how they manage this.
Other ideas from small businesses and social experts welcome!!