I lived in Paris and experienced the velib first hand. I suspect it won't work in London because:
* They are not putting enough bikes in. It has to be SWAMPED. Paris works because you don't have to know where the bikes or docking stations are - they are everywhere.
* Paris is cheap beyond chips. 29 euros for a year's (sic, year) pass. Ie 20 quid. Every journey (under 30 mins) then free.
* Paris is compact and dense.
* Paris (inside peripherique) has no crime, graffiti or feral hoodies.
* Paris has no HGV or large delivery lorries.
None of these logistical details, which make the difference between winning and losing, I suspect Boris will put his mind to.
I used the Paris bikes for a week or so back in 2007, when there were still bugs to be ironed out but the concept had obviously been successful.
The main problem was the return of bikes - many, many peple all make the same types of journey at the same time, so that if I wanted to ride down to the Louvre from the Science park in the morning I'd struggle to find a bike at the start and then struggle to find a free bay at the end. The situation reverses in the late afternoon.
There were vans travelling round servicing the bikes and 'seeding' the racks, but I would argue you need a far greater number of bays than bikes to make sure you don't have to cylce further away than you started in order to drop the bike. Is there space in London, near tube stops or attractions, to locate these? This happened a couple of times in Paris, once by the Eiffel Tower and once near a restaurant we were meeting in (forget where).
Re. the inability to lock the bikes to anything else, the point is that there should be enough bikes to dock one, do your shopping, walk the few hundred yards to the bays and take another. As you only have 1/2hour of hire time (the charges are really there to discourage longer hires) in my opinion it's really intended to support 1-way hire. Encouraging round trips would mitigate the need for more bays, but I think commuting was where the problem lay.
Of course, this is all Paris' interpretation/implementation, I suspect London may need to do things differently. I worry about how the cycle paths would work, Paris kerbed off set cycle lanes on the major roads, would that work in London, or would we end up with touritsts riding on pavements?
Also, the Paris scheme is essentially funded by advertising rights on the bays, so expcet loads more hoardings about the place.