You all do realize these are Class 4, and they are going to be very slow for booting on an RPi. You would be well served to get a class 10 for £10...
I think that anyone planning to buy an SD Card should read the extensive thread on the subject, particularly the posts from Chromatix here:
My understanding is that the lower operating voltages of Classes higher than 4 would need changes to the GPU firmware, and some settings on the Linux drivers changing. This isn't something that I would be wanting to muck about with when trying to get my first RasPi up and running. I'm not even sure that the GPU firmware can be altered by users - it may be a Broadcom-only thing.
It would be good if Chromatix or someone could add some SD buying advice to the wiki.
I would suggest that buyers of a particularly nervous disposition check for a verified SD card in the list on the wiki here:
Also, everyone should remember that speed and latency are not the same thing. I understand that the higher class numbers are designed for speed e.g. writing a huge photo from your camera quickly, rather than latency which is more important for this kind of application (i.e. acting as the HDD for an operating system).