As a developer and consultant, I want to be able to understand the impact of new features included in the next release of Salesforce as soon as possible, not only to learn of new leverage opportunities to pass on to my customers but also to build scenarios for negative impact on current implementations. I would like to know what are the new features to be included in the Salesforce Spring '14 release.
You have to wait for the release notes which will be posted here or eventually here. Salesforce.com has a "roadmap" of features, much like any company would for planning, but I know that the plans change and some features never make it, just like happens with any company. Any features that you see/hear about at Dreamforce or find out about before they are out, even if provided by Salesforce.com itself always have the Safe Harbor statement attached to it.
You can look into participating in the Spring '14 preview to get an early preview.
Sometimes you can get an idea of what is coming in the next release by looking at the Ideas Exchange, their status and the comments from Salesforce: https://success.salesforce.com/ideaSearch?filter=Under+Consideration e.g. Floating report headers are coming in Spring '14!
From today, you can read all about Spring 14 new features in the release notes!