Our latest event “IT-Pro Chalk Talk” co-hosted with Winsec & IT-Talks was very interactive and several questions arose during that session. 
http://www.pro-exchange.be/blogs/events/archive/2010/02/04/event-it-pro-chalk-talk-session.aspx

Question : Exchange & Backoffice apps Remote location vs Datacenter (decentralisation vs consolidation)

Answer :

This is a difficult question to tackle because it all depends on the applications you are using.
Also important is the impact of unavailability, what money does the business lose when applications are unavailable.
What does it cost to have good WAN connections, in some countries they are very unreliable.

Let’s try to give some good directions:

WAN Considerations in Centralized solution

• Monitor current Bandwidth usage. (Tom Decaluwe wrote a good blog post on reading correct values out of Cisco routers : http://trycatch.be/blogs/decaluwet/archive/2010/03/09/snmp-read-ifinoctets-gt-great-trend-but-what-about-the-absolute-throughput-value.aspx
• You might need to look at WAN Optimizers to more efficiently utilize your WAN connection (for some protocols you get huge benefits)
• Or use Caching solutions
• Upgrading WAN might be too expensive depending on your location
• Satellite connections for WAN connectivity have high latency but might provide better throughput
• Are you losing money when WAN is unavailable, can you provide a backup WAN connection
• Use the best protocols to connect to the centralized environment (for example Rich Outlook Web Access uses more bandwidth than normal Outlook
• Do pilots to verify if it can work

Considerations in Decentralized solution

• Hardware costs will be much higher
• Management costs will be much higher (who will manage the system administration / backups / … )
• Application availability when WAN fails
• Decentralized High availability is too expensive

Conslusion:

Money, usability, availability and manageability are the keywords to get started