Google talked about the developer preview of Caffeine in its blog in the month of August. The new technology will improve the indexing infrastructure of Google. After receiving positive feedback on Caffeine, Google has now moved on from the developer preview stage to making the technology live at one data center. The new technology will benefit a small percentage of Google users in their regular searches.
Although, the Caffeine will go live at one data center but the full roll out will be done after Christmas only. With the one live center, the Google team will continue to collect data for improving the technology.
Most of the searchers will not be able to notice immediate changes with Caffeine but as more feedback will be collected, improvements will be made and the stress on webmasters will be minimized during holidays.
If you are still interested in giving feedback on Caffeine to Google team, here's a link to original Google Caffeine post telling you how to go about the process.