I suspect that the logistics of buying a share to learn in will eventually prove unworkable (except for microlight schools, where in many this is the norm, and therefore they are set up for it). But, by all means prove me wrong - I won't be offended!
For building up experience later however, I think there's much to be said for it. Whilst not for that purpose, I spent £2k on a PA28 share a few years ago, and since have flown it about 30-35 hrs pa - for which I pay £60/hr (actually £50/hr + £30/month). Rental on a similar aircraft locally is around £120/hr (I don't live in a cheap flying area).
So, over one year / 35 hrs, you could reasonably argue that I broke even - but subsequently, my hourly flying cost is roughly halved compared to renting. Plus, I can should I wish put the share up for sale, and probably get my £2k back.
And you probably get to fly a better aeroplane, as well as gaining the experience of managing an aircraft as an owner - that is worth a lot. But, it does make a point - joint ownership means joint risk, joint cleaning duties, joint helping-with-maintenance-to-keep-the-costs down. You are basically trading time and risk for the money saved, it's not a one-way street.
G