Hi!
As far as I know Lycos uses PHP.
There are a lot of Russian web sites - some of which are very famous over here - that leverage PHP.
Sites that can afford it use custom CGI solutions that usually fit their needs. For instance Amazon.com is using obidos which is very fast, but again, it's a custom CGI solution all done in C. If you need good speed, you can just rewrite your site in C and get better speed in almost every page.
Frankly, I don't see any reason against writing your site in PHP. Given a custom hosting option with custom hardware, special Zend software such as Cache, your site can fly, even if it's close to Microsoft's in the degree of its complexity.
You can take a look at this to see the share of PHP vs other Apache modules:
http://www.securityspace.com/s_survey/data/man.200201/apachemods.html
On php.net there has been some mention about sites using PHP.
Hope this helps,
All the best,
Stas