More anecdote I'm afraid, but when the company I work for implemented the scheme I know at least 3 new cycles appeared in the racks at our sites in Dundee and Edinburgh. I don't know the owners, so can't say for sure whether they were existing cyclists, but even if they were they weren't commuting cyclists before the scheme.
Of the 'regular cyclists' that I know (myself included) none availed themselves of the scheme because our company chose to retain to themselves the VAT, with the excuse that 'you will save about 30% anyway, so why shouldn't we make something on the deal as well'. They also chose to use the Halfords scheme, with some credit charge thingy in it, which meant I got a bike cheaper by buying last years model from Halfords myself...
I can provide a contact name by PM if you are interested in trying to get some official numbers on takeup (I work for a large government funded organisation concerned with the supply of drinking water and sewerage services).