O Hai! I can haz toolbox ?

First thing was to find a set of tools, widgets, plugins, things that suck ram and displays what I'm looking for in the laziest way possible, because this after all has to remain funny.
First tool is telnet. Here's an example:

gregg@centralperk:~$ telnet www.facebook.com 80
Trying 69.63.184.143...
Connected to www.facebook.com.
Escape character is '^]'.
HEAD / HTTP/1.1
host: localhost

HTTP/1.1 302 Found Date: Mon, 20 Jul 2009 22:34:18 GMT
Server: Apache/1.3.41.fb2
Location: http://www.ocalhos.ocalhost/common/browser.php
Connection: close
Content-Type: text/html; charset=utf-8

Connection closed by foreign host.

Well, yeah, that's the BOFH way - painfull, h4x0rZ and not eyecandy at all. On top of that, you would forget to set the host string every second attempt, and would get no response just because of that.
Big up here for the facebook sys architects here that found important to mention they had patched Apache. (...to the morons that found important to read their server header, and obviously I belong to that aforementioned category of deviants).
Well, that being said, it is not handy at all, so I found something else.

After messing a bit with buggy expect scripts of my own to automate that, I found this kneat Firefox Extension that does it for you, all the time, and displays the result in your status bar. Me likey !
Now I can't help, whenever I go to a website, I'd take a quick look at what ServerSignature string it is sending in its HTTP headers.

O Hai ! I can haZ statz ?

Now the thing I was interested in was to see some actual stats on what WebServers were used and a few comments on why if available.
Again, the folks from Netcraft - by the way hats off to you folks for the excellent work you've been doing this past decade with NetCraft - have gathered some precious data around that.

The google webserver army

At some point, I came accross this blog post from dotcomunderground.com which is particularly interesting, as it lists all webservers used by most of Google's ASP apps.
Useless, but definitely worth reading :)

Conclusion

As a conclusion, there is some pretty amazing stuff to be learned by just paying close attention to tiny details. Very likely, one would prefer one webserver instead of another for pragmatic reasons, which is the reason why it is always good to know what alternatives you've got. This is how you'll certainly one day evaluate the likes of Nginx, Resin, thttpd... because each one of these might have its specificities that makes it worth using.
Eventually, you'll come across funny stuff, such as people trying to show off by stating their webserver is a KitchenAid2000 running on a Whirlpool IP OS 12.5 to state their l33tness out loud, but if there's one thing for certain: turning your ServerSignature off is a good security measure, and setting it to a fancy value brings attention, so you might not want to stand out in the crowd an get pwnd just for fun of it :)
Oh and yeah, I found particularly funny that USA's NSA's website runs on Microsoft-IIS/6.0 servers. Maybe it's just a part of it, but I can't help thinking that if I wanted a honeypot, I'd use that ServerSignature on it.