I spoke to a friend of mine some time back who has done some mining, and
what I remember about what he said was:

 

Originally, the problems were pretty easy, but they get harder as each
problem is solved.  Now the problems are very hard, so that at this
point, you almost have to buy an asic-based 'solution', because
otherwise the  cost of electricity will wipe out your bitcoin 'payment'.

(Interesting that some of the guys who make and sell those ASIC
solutions will accept bitcoin in payment)

 

The sad thing is that the problems you are solving have no 'socially
redeeming value' - you are not solving any real-world problems.  I think
you aren't even computing pi to a quadrillion decimal places ;-)