aaahhhhh thanks for all Michael, I've forgotten the problem of ID generated by media upload...
It's a very big problem for me because we are soo many contributors on our blog, and I have customized permalinks (tags, categories, posts, etc...) which could conflict each other (sorry for my bad english, I do the best to explain), so the POST ID was a good solution for me, but we have too longer ID, for instance :
http://mydomain.com/11954-my-blog-post/
Soon IDs will rise up to 100 000................
So there isn't an automatic solution for this problem ? It's difficult to impose to authors to put manual IDs, because it could generate conflicts too....