empty pages

In order to improve site performance I implement Cache module for my shop, which based on prestashop.
Cache module based on Pear:Cache_Lite engine and able to store cached part of pages to file system.
My estimation in such performance improvement – 2-8 times, depends of you site and database.

Also for support cache module I implement «preaching sub module» it run every night and prepare caches which will be used during day.

UPDATE (13 Jan 2010)

Google performance overview

On average, pages in your site take 1.7 seconds to load (updated on Jan 4, 2010). This is faster than 74% of sites. These estimates are of low accuracy (less than 100 data points). The chart below shows how your site’s average page load time has changed over the last few months. For your reference, it also shows the 20th percentile value across all sites, separating slow and fast load times.