HTTP header order is often characteristic of a web server. The opensourceparking.com headers say Apache, but have the Date & Server headers last, a pattern which is identical to the lighttpd response and entirely unlike a typical Apache response. The etag is also not in Apache format, and matches the lighttpd format:

http://www.lighttpd.net
HTTP/1.1 200 OK
Content-Type: text/html
ETag: "-968787920"
Accept-Ranges: bytes
Last-Modified: Tue, 27 Mar 2007 20:27:33 GMT
Content-Length: 3665
Date: Sun, 01 Apr 2007 10:23:53 GMT
Server: lighttpd/1.4.13
http://opensourceparking.com
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
ETag: "-2025453841"
Accept-Ranges: bytes
Last-Modified: Mon, 01 Jan 2007 15:24:53 GMT
Content-Length: 2912
Date: Sun, 01 Apr 2007 10:24:30 GMT
Server: Apache/2.0.54 (Debian GNU/Linux); Hello Netcraft!
http://www.apache.org
HTTP/1.1 200 OK
Date: Sun, 01 Apr 2007 10:25:00 GMT
Server: Apache/2.3.0-dev (Unix)
Last-Modified: Thu, 29 Mar 2007 01:00:37 GMT
ETag: "921bbd-3e5f-486b9740"
Accept-Ranges: bytes
Content-Length: 15967
Cache-Control: max-age=86400
Expires: Mon, 02 Apr 2007 10:25:00 GMT
Vary: Accept-Encoding
Content-Type: text/html

Perens downplayed the significance of Microsoft’s market share gains because they relied upon parked domains. “This is an ‘appearance’ change only, because the sites involved have no content,” he wrote in announcing the service. “But managers believe figures like those in the Netcraft report, and act on them.”

Apache is used by domain registrars Register.com, 1&1 Internet, Dotster and DirectNIC, while Demand Media/eNom uses Windows Server 2003.