Pesos - We are including a VSS plugin for Windows Server Backup (similar to what was included in Exchange 2007 SP2). The only limitation with this tool is that it is not DAG aware (meaning you can only backup the active databases).
Matt - To put it simply you need to move away from PSTs. Larger mailboxes are the answer here. In addition you can leverage, single item recovery, and our messaging records management 2.0 with a personal archive mailbox to retain needed data and manage your quotas.
Nick - We haven't released an Exchange 2010 version of the storage calculator, but I am working on its development. When it is released we will post it to the EHLO blog.
Glen - Single item recovery is just one piece of the puzzle in terms of moving toward having Exchange as your backup solution. You also need multiple copies (covered through our mailbox resiliency features). For the scenario you highlighted, you could leverage a lagged mailbox database copy and control when transaction logs are replayed into the lagged copy, thus providing you a means to recover from logical corruption (provided you know when the corruption occurred).
Karsten - messages/items that are infected by viruses are hopefully quarantined / cleaned at the transport layer. The those quarantined messages would never get to the mailbox. If on the other hand, the infected message got through to the mailbox, it would be treated like any normal message. If there is an AV engine on the mailbox server, it would be able to quaratine or clean the message.
Ross