I recently took a trip over the English channel from Calais to Dover on a P&O ferry and noticed the vending machine shown in the picture on the right from which passengers can get English SIM cards from different operators for their time on the island. Since no registration is required in the UK when buying a SIM, it is already activated and can therefore be used right away.
Note that only UK operators were offering their SIM cards in the machine, French SIM cards were nowhere to be seen. This could be because the ferry was operated by an English company or maybe because identification is required when buying a SIM card in France. Maybe it's also due to the lack of real competition in the wireless market in France. Hard to tell.
However, upon my return to France, I noticed that in some train stations and also in some supermarkets, Virgin, a MVNO using Boyugues' GSM network sells 'mobile phones to go'. The box says they can be used right away but a copy of the passport has to be sent to them within 7 days. The text on the box also suggested that topping up the account might also only be possible once the registration has been processed. I wonder if that is a creative way to comply to government regulations or to ensure people send in their details.
Anyway, I hope that SIM card vending machines do make it into other places such as airports as well, it would significantly reduce the effort to get a local SIM card for mobile Internet access when arriving in a country.