The Schengen Agreement (named after the village Schengen, a village directly on the three border point of Germany, Belgium and Luxembourg, where it was signed), as far as travellers are concerned, basically dissolves borders control within all member countries. Once you have entered the Schengen area, you may travel freely within all member countries for 90 days in a six-month period without having to cross passport control points. If you are a citizen of one of these countries, you can travel within all member countries without any limits and without a passport. Therefore, the Schengen agreement extension will reveal to be an hassle for non-EU passport holders, as the nearest border to cross and back (for a new 90 days) will be less reachable.
For Canadian, US, Australian and New Zealand passport holders, the remaining options will be to cross to the United Kingdom/Ireland or go down to the Balkans, the Ukraine, to Turkey or to Morocco once you're nearing your 90 days limits within Schengen. The UK border is probably the worst of these options in terms of chances of being sent away or denied entry.
Notice that sometimes within Schengen borders, especially while going along by train, policemen do come on board and ask to see your documents. Usually it's trouble-free, but they tend to harass Balkans and Turks more often than others.
28 European states have signed the agreement, including most European countries and three non-EU countries (Iceland, Norway, Switzerland). Ireland and the United Kingdom did not sign the treaty. 24 of these countries have implemented the agreement so far.
- Czech Republic