It should do what the name says, speed up your pages. Google said:
We're starting with more than 15 on-the-fly optimizations that address various aspects of web performance, including optimizing caching, minimizing client-server round trips and minimizing payload size. We've seen mod_pagespeed reduce page load times by up to 50% (an average across a rough sample of sites we tried) -- in other words, essentially speeding up websites by about 2x, and sometimes even faster.
My team tested it but we have not yet activated it or made a decision if we will.
We all know how obsessed Google is with speed and how it may play a small part in the Google ranking algorithm. But at the same time, there are some concerns.
A WebmasterWorldthread has some of those concerns:
Great stuff provided it does what it promises, my only concern is about installing any thing coming from big bro on my servers. We'd better check sources before installing.
Also, the mod does a fair amount of page code 'rewriting', something once considered absolutely not okay when browser-based because of the high likelihood it messed up your original code -- alignments changed, ditto font and image sizes, etc.
On the flip side:
I see no reason that this would send anything back to Google. Google have never lied about what Chrome does - and you can turn it off.
So, will you use it? Take my poll:
Forum discussion at WebmasterWorld.