According to royal.pingdom.com, 22 of google's 49 products are classified as beta, including gmail.
http://royal.pingdom.com/2008/09/24/why-is-almost-half-of-google-in-beta/

Paul McNamara from networkworld got a reply from google.

In part it said:
"We believe beta has a different meaning when applied to applications on the Web, where people expect continual improvements in a product."

http://www.networkworld.com/community/node/33131

I'm supprised that the figure is as low as 45% :P I thought it would have been higher than that! Even 57% seems a bit low.

I'm surprised how few Google products they checked.

Wikipedia (http://en.wikipedia.org/wiki/List_of_Google_products) lists over 100.

I remember that Google Answers came out of beta on the same day that it started to contain AdSense.

This makes me wonder whether the "beta" status doesn't just refer to how the product works for the user, but to how the product is "performing" according to Google's corporate goals.

Maybe Gmail is losing Google too much money for them to take it out of beta.