I use the Santander hire bikes regularly to ride between Victoria and the office. The current manifestation of the app is great - you can check there are actually bikes in the station before you get there and request a release code, so you can just walk up, dib it in and be away in seconds.
I amuse myself by looking for patterns in the release codes - not much scope for variety with a 5-digit base-3 system but I did enjoy the fact that yesterday the codes for both my morning and evening journeys were palindromic. Even better, one of them was the roadie's release code - 12121