What is the difference between a Mac mini and a Mac mini server?

Apple sells two Mac minis; one is a server edition, the other is a standard Mac mini. What are the differences between the Mac mini and the Mac mini server?
I know that the server doesn't have an optical drive and runs a server edition of OS X. Besides this, what are the other differences? What is the advantage of buying a Mac mini over buying a Mac mini server? (besides, of course, that the server runs OS X Server, and one is faster than the other) Will the server last longer, be able to handle running 24/7, whereas the standard one won't?

Comparison of Mac Mini and Mac Mini Server (as of mid 2011)

Processor:

• Server: Quad core i7

• Mac Mini: Dual core i5

  • The base model of the Mac Mini does not support AES-NI which is recommended when using FileVault 2.

Graphics:

• Server edition and Mac Mini base model: integrated HD Graphics 3000

• High end Mac Mini: dedicated graphics, AMD Radeon HD 6630M with GDDR5

  • Note: This is very recommended for Lion on large external displays. The integrated HD Graphics 3000 do not perform well in Lion as of 10.7.3 - even on my 15'' MBP.

Hard drive:

• Server: 2 x 500GB at 7400rpm
• Mac Mini: 1 x 500GB at 5400rpm - and thus quieter

Optical Drive:

• Server: none
• Mac Mini: none

Weight:

• The server edition weights 0.3 pounds more.

Video, Audio, Network, Dimensions:

• same

The difference is a few hundred bucks.
Kidding aside, though, there are several differences between the two models. Some differences are that the server version runs off of a Quad-Core i7, has dual 500 GB HDDs and a more powerful graphics processor.
Check out the side-by-side comparison here.