GoogleTechnology is amazing. Enough for some people to forgive that GoogleSucks.
Their technology is mainly in the ability to package UserInterface to new levels of usability, all the time without having to use the NextBigThing in computing.
In the case of GoogleMail? (it does not use ExtensibleMarkupLanguage WebServices), there is an insider report on it at http://www.eweek.com/print_article2/0,2533,a=125289,00.asp