Winter is just around the corner, and so is the next version of Salesforce.com!
Currently if you are using Salesforce.com, and have multiple instances such as a production and sandbox environment you may be running two different API versions. The sandbox may be at version 29.0 which is winter ’14, when production is running 28.0 Summer ’13. This can cause issues with change sets that contain items created in the 29.0 version environment. Production environments will see the new version in October. Below is a handy link that can help you identify when your version will see Winter ’14.
For those curious in what’s new for Winter ’14: