Replying here. There are free alternatives. But first of all, I have a very powerful machine (a lot of CPU power for a single laptop, a decent SDD space) for a reasonable price. Then, I am very used to the mail client, the keynote program, the numbers program, iphoto, etc. For the rest, since I am mostly using a shell (programming, writing letters, etc.), it does not count :D
One strong point is the fact that it works out of the box when connecting my computer to a projector ;)
I can of course change, and I will if necessary. But for the moment, I am happy with mac.