Google Caffeine is now out of beta and Google has deployed the new search technology to at least one of their datacenters. Caffeine is really just another search algorithm update with a focus on optimizing speed and the efficiency of the delivered search results.

Caffeine is about boosting speed, performance and relevance in the Google Search Results. Consequently, it would be a prudent strategy for webmasters to further optimize their sites for quicker load times. The easiest way to optimize page load times is to optimize images to be smaller sized files - meaning fewer kilobytes.

Page weight has always been a key tactic in on-page SEO. If you think about it from the perspective of your users, you don't want to wait for a website to load. Most of the time your website visitors are not sure that they should even be visiting your website - so they aren't going to wait around for your slow loading hi-resolution marketing images to load.

Having a fast loading - Google Caffine friendly site starts with good website design. Your web designer should know what images to export as .PNG, what color depth to use, and for JPG images, they should likewise save them in a web friendly - light weight and with optimized file sizes. Your ideal page size should be around 300kb, and definitely less than 400kb. That page size includes images, text, javascript, css, and flash, all of which add weight to the page.

You can measure the weight of your pages by using the free Firebug Extension for firefox.

Google Page Speed Best Practices
14 Rules for Faster Loading Web Sites