Overnight demand is substantially less than daytime - last night's demand in the UK was about 20% lower:http://www.gridwatch.templar.co.uk/index.php

The grid would prefer a another demand curve, so overnight charging is helpful.

Is that going to be the same when say 15%-20% of the nation plugs in a car every evening - its going to the surge when people go to make a cup of tea when the adverts are on during coronation street look tame.

Car charging is a steady, predictable usage of electricity. People don't all arrive home at the exact same time.

Additionally, being giant batteries, electric cars have the means to charge when most advantageous to the national grid. Most electric cars already have an option to wait to charge until off peak rates happen. (Off peak rates being cheaper because low overall demand.)

But electric cars may be useful to the grid as giant surge protectors for things just like that cup of tea electric kettle break. Under some of the "smart grid" proposals, the electric companies would be able to not feed electricity to a vehicle in those brief moments of high demand on the grid, prioritizing immediate needs like people's kettles. Furthermore, "smart grid" ideas could even use electric cars as battery backup options, "leasing" already stored energy back from the car and paying it back later, as changes in demand happen.

Even if some of those "smart grid" ideas don't get nationalized, you could still theoretically take advantage of some of those kinds of things in your own home.

So if anything, electric cars may be surge stabilizers rather than surge causers.

Street parking solutions are being proposed. Many streets already have power to the street (street lamps and similar street furniture) and chargers become the new parking meter. Also, there's experiments in street-installed inductive chargers (like the wireless chargers you can buy for many phones these days) and even companies exploring the logical extreme of street-level inductive chargers the "power road" (where the car can draw an inductive charge even while driving), which seems unlikely to be pragmatic but still interesting to experiment with.