I will sing the Smarts praises all day long. I love them, great fun to drive.
That said, this was when we hired one in Santorini last year (see photos).
http://i93.photobucket.com/albums/l7...i/IMG_0985.jpg http://i93.photobucket.com/albums/l7...i/IMG_0984.jpg http://i93.photobucket.com/albums/l7...i/IMG_0987.jpg
Not entirely sure how happy I'd be to use one on UK roads, but I really enjoyed driving it, so easy to use and so much fun. You could easily get 3-4 bags of shopping in the "boot" and I'm sure a seasoned expert could squeeze in more. As for getting in and out...
As you probably know (I do go on about my defining feature) I'm 6ft 7 and I had no problems getting in and out, and found a comfortable driving position really easily - more so than in several "larger" cars I've tried in the past.
I've tried to persuade LadyWayne to get one instead of her current car, but she, like me occasionally needs to carry more than two people, and more often uses the car to carry more than the weeks shopping.
If it's just for a runabout though I'd say go for it!