Google is testing a service to serve modified versions of customers' pages. These pages may be served from Google's various servers worldwide.
http://code.google.com/speed/pss/

Rewriters enabled by default:
   Combine CSS
   Combine JavaScript
   Optimize Images
   Resize Images
   Move CSS to Head
   Proxy Images

Other rewriters:
   Optimize JavaScript
   Proxy CSS
   Proxy JavaScript

excerpts from faq:
There is no https support. Blogger, Google Sites and Google App Engine are currently not supported. Flash, streaming audio and video content are not currently supported. Page Speed Service does not support reference domains that have only an IPv6 address.

So many of Google's own pages are slow. Why don't they fix them before they modify other peoples pages?

I have applied for the beta.

> So many of Google's own pages are slow. Why don't they
> fix them before they modify other peoples pages?

That's a fair comment, but I think Google has made enormous progress in recent months.

Knol used to be incredibly slow and extremely clunky. Now it's just "somewhat" slow and "a bit" clunky.

Blogspot.com used to be slow as molasses, but it's now quite reasonable. If it had been this fast five years ago, WordPress.com might not have become a viable competitor.

Google image search is now astonishingly fast.

Docs has become pretty fast too. Maps is usually very good, just occasionally a tile gets delayed.

Heck, even Orkut runs fast nowadays, and that's saying something!

One of my sites, www.monitor.edu.pl, uses the service since yesterday. It was really easy to set up, but it would be nice to have an option to configure it so it does more cacheing.

Well built sites sometimes become overall faster, but practically slower such as:
http://www.webpagetest.org/result/110731_SD_7f37a48a626dadc42891f0ad9cf0c040/

Other sites will stop working after being optimized such as:
http://www.webpagetest.org/result/110731_1T_fff68f52a1fe4a5dd47f2eb2b30f2edc/

Just thought I would share this XD