I too looked into buying a share, and ummed and ahhhed for a while, and didn't do it.
The problem I have at my local club is that it is far too busy to get a plane in short notice, i.e. within a week. This means I either take an extended lunch, or just don't fly. It is more often the latter. Taking the plane for a weekend or for the whole day is just out of the question.
I did look into a share in a complex single, and once I delved into the costs, it started to look quite expensive. Wet hr was £80, and monthly costs were £300. Adding this all up meant that it was a false economy, I'd be needing to do an awful lot of hrs to make it cheaper.
The advantage was that the three other members in the group didn't really ever use the aircraft, and none of them had ever taken it away for a weekend. Something which I liked the sound of, so from a logistical point it was much better. I reckon the only reason I didn't do it was it would take about 90 mins in the car to get to the airfield.
Now this does sound expensive, and I've seen much cheaper options - an Arrow in North London and no joining fee etc, and there is a chap on this site with a couple of 152s in Oxford that look quite tempting - very cheap hrs. The only problem with these is the length of time is takes to get there in the car.