For the Salesforce Spring 2013 release there are the headline additions and updates for developers:
1) Tooling API
2) Connect in Apex
3) Force.com Canvas Updates
4) Connected Apps
But what I always get excited about is reading the details about the little improvement gems that get sprinkled into Apex, Visualforce and the APIs. Here are the ones that caught my eye in this release.
1) Additions related to TimeZone will be helpful. There is a new class called TimeZone that can populated by a call to UserInfo.getTimeZone(). Once you have an instance of that TimeZone class, then you can use the new methods getDisplayName(), getID(), getOffset(), and toString() to get quick details about the timezone.
2) Another simple addition that will save a query is the UserInfo.getUserEmail() addition. As developers we are trying to save queries anywhere we can in complex orgs in order to stay under the governor limit for the number of queries. Every little addition like this helps.
3) Setting ID field on sObjects for updates is now possible as it is no longer a read-only field. In some ways this may not make sense as you normally query out your sObjects so you already have the ID field set properly. But when working with external data that is related to your internal data this can come into play. You may have built up a series of sObjects from external data and you may even know the Salesforce ID as it may be stored in that external data source. Now the sObject can be built and the ID field added to it without needing to query the sObject from Salesforce.
4) This next one does not help me in any way except that the page is no longer locked, but it is good to note. When tests are run the page will no longer be locked and you will need to manually setup debug logs to capture trace information before the tests are run. The developer console seems to be the place to turn to more and more when running tests as logs can be automatically found there.
5) I have done a lot of work with the Metadata API in trying to mass create custom fields and also dynamically figure out changes within an org. It is important to note that within the Metadata API that the SecuritySettings and MobileSettings are removed and that new options like AddressSettings and CaseSettings will be in the settings directory.
6) This one is only in Beta but some State and Country pre-defined lists are now available. It is great to know that usually within one or two releases that these Beta features will be fully available.
These little items do not get the grand attention in the headlines, but it is continual improvements like these that keep me excited as a Salesforce developer because I see my productivity on the platform improving.
Keep sending Salesforce the ideas for new enhancements that you need. They are listening!