Here's what I'm excited about in Spring '13. if you haven't done so already, the Relase Notes are always a good read.
Salesforce Side Panel for Outlook
Pretty big win here for all you Windows/Outlook users out there. See: Introducing the Salesforce for Outlook Side Panel
New Controls for Sending Email
This is great. Now in your Sandbox Salesforce gives you the ability to control the type of email you can send Org-wide. With the click of a button you can now disable all outgoing email, allow only system email, or allow all email. This will surely come in handy when testing.
Track Contract History for All Statuses
The first time I worked on a Contracts implementation my mind was completely blown (and saddened) by the stange system limitation that wouldn't track field history for Contracts in a 'Draft' status. Finally, you can track field history regardless of status. Win.
This has convinced me to finally bite the bullet and pick up an iPad. This has also convinced our EVP of Worldwide Sales that he should have one as well.
Add Report Types Faster
A small enhancement, but one that will surely make the lives of the hardcore report builders out there that much better. I love Salesforce.com's commitment to user experience, and it's the small changes like this that really add up to create a better experience for their end users.
D&B DUNSRight Account Matching (Beta)
This is fantastic. You can now scrub your Account records against Dun & Bradstreet to keep them clean and up to date. We just did this (manually) at Iron Mountain, and overnight it exposed several hundred thousand (yes, several hundred thousand) duplicate Account records. Brilliant.
Granting Access to User Records (Pilot)
You can now grant users access to your user record without the need for the 'View All Users' permission. I like this. Recently there has been a lot of Chatter on Ideas asking for more granular/segregated user permissions. This is certainly a small step in the right direction.
New Classes and Methods
getCaseIdFromEmailThreadId method. You can now use an Email Thread Id to retrieve the related Case Id. This is great for all you Service Cloud users out there.
As far as the new time zone methods are concerned... I work at a company that uses one instance for our entire worldwide deployment, and these new methods will surely prove themselves useful.
With Force.com Canvas it's now possible to integrate just about any application with Salesforce.com, regardless of language or where the application resides. I think this is going to be wildly popular, and I'm beyond excited to see what companies do with this.
See: Create Force.com Apps Anywhere With Force.com Canvas
State and Country Picklists (Beta)
There was a lot of buzz about this at Dreamforce, and I'm beyond excited this is finally here.
Just as it sounds- there are now pre-defined, standardized state and country picklists. This had nearly 50,000 points on the IdeaExchange.
Field History Tracking Deletion
I don't think I ever realized this, but if your Org was created after June 1, 2011 Salesforce automatically deletes field history after 18 months. Now all you have to do is pick up the phone to disable the auto-deletion.
Sandbox Email Deliverability Default
Related to the new Email controls, Sandboxes will default to only send system email. I actually like this, as it eliminates the potential to accidentally email leads/contacts from your Sandbox.
Record Type Available as a Cross-Object Reference
This is great. An object's record type is now available as a cross-object reference (i.e. Lead.RecordType.Name). Another small win that will make the 'True to the Core' fans happy, I'm sure.
And there you have it. What are you excited about in Spring '13?