I tend to 'counterspell' in two ways.
Either I ready a Lightening Bolt or one of its derivitives (Chain Lightning, Cross of Lightening, Electrical Deluge)... (yeah I know swatting flies with a Howitzer...)
Or I hit it with a Dispel after it was cast...
Generally I have found that shutting them down the 'old fashioned way', i.e. with death, is a lot easier in the long run than trying to stop each and every spell... However I can see the use of stopping a few of the nastier spells. The problem comes in how do you decide what spells to stop?
For instance, my Sorceror is often Hasted. So I get 2 castings a round. Do you counterspell the first spell I cast, or the second? Can I ready two actions to counterspell? (one from the Standard action, one from the Hasted partial)