Much has already been said about the Spring 09 release:

Official Release Notes

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Perspectives on Salesforce

Jeff Douglas

I won’t elaborate much except to say that I am specifically looking forward to:

• Snapshots of report data; trending of reports (instead of copying the records of an object like in an analytic snapshot, it just copies the report data)
• Delegated data administration (ability to grant granular access for a profile to specific object, regardless of hierarchy – for instance HR to payroll object)
• Email to case as a service (no box required behind the firewall)
• Text() functions for picklists (I voted for this one so I take all credit :))
• Report formulas vastly more capable (it looks like the formula has the same capabilities as a custom field… all I can say is YES!)
• Cross object field update for custom objects (but not for standard?  field update can update a field on a related object so long as it is a custom object)