PHPEverywhere has some information this morning clipped from something that Zeev wrote talking about PHP 4.1.0 and Windows.
Revolutionary performance and stability improvements under Windows. The multithreaded server modules under Windows (ISAPI, Apache, etc.) perform as much as 30 times faster under load! We want to thank Brett Brewer and his team in Microsoft for working with us to improve PHP for Windows. This means that ISAPI is considered to be production quality?
Yes, even though quite a few modules inside PHP are not yet thread safe, so if you use them, it'd crash.

I thought this was an interesting note, considering how much of the PHP world uses MySQL happily. MySQL.com has a link to the InfoWorld 100 list of "the top 100 companies showing the greatest IT achievements during the year". Happily enough, Yahoo.com was ranked #27 on the list for thier use of MySQL in their financial section. Betcha didn't know that, huh? They use MySQL as a backend for most of their financial site....maybe they'll catch on and convert more of the site...