It's not like it isn't already linked all over the place, but it is still worth a mention. Some of the things I've tried so far:

• Solving the quadratic equation
• Why stop there?
• Great wall of china divided by earth's circumference
• Calories in a peanut
• Determinent of a matrix
• Matrix dot products

Some results are confusing:

• Derivative of y=x^2 why doesn't it also display the succinct 'implicit derivative' 2x result you get from the y=x^2 page?
• And Integrate y=2x, doesn't really do anything, yet we've just done the answer above. (Ah, it's because you need to do integrate 2x dx)

And it doesn't do well with misspellings:

• Fibonnacci sequence vs Fibonacci sequence

And it's limited in some Engineering areas:

• It does springs and columns
  
• But not plates, pressure vessels or beams

Ack, this was only meant to be a quick post, but have gone on too much already. Lots of fun can be had with it anyway.