Here is another great article by MSExchange team touching base some of the mostly asked questions in Exchange 2010.
Simplifying and reducing the complexity of messaging environment while making it full redundant and faster is the most impressive part of Exchange 2010. You don’t need to deploy Exchange in complicated SAN.
Use DAS ( direct attached storage ) and simplify the operations of Exchange by taking dedicated SAN personal out the picture and have your Exchange administrators to have full responsibility and control.
As you can read more from bottom link most of these improvement are targeted to lower the cost, simplify the application deployment and operations while providing the best messaging experience.
Some of the highlights from this article
1. Exchange 2010 supports up to 100,000 items per folder,Remember Exchange 2007 supported up to 20.000 items per folder.
2. SIS is gone.Exchange 2010 does provide 20% database compression for HTML/Plain Text Messages
3. Simply the deployment, no more dedicated SAN person into Exchange deployment scenarios, simply use DAS to deploy exchange.
4. What is “backup less” Exchange ? With the ability to have multiple copies of each database, along with features such as single item recovery and lagged copy support, you might not need to use traditional backups
Exchange 2010 Large Mailbox Vision Whitepaper