I burned the east disc on a verbatim DVD+R DL using gburner.
The update went fine and I had a lot of new streets in my area. The only problem was that the system could not find any routes to a destination more than a few kilometers from where I was.
I then decided to put back the old maps and it was refused, which is normal (from what I read so far). I decided to change the language to english (french previously) so I could explain my problem better here and the system restarted and said to insert the appropriate disc. I took that opportunity to give it the old one and it rolled back to the old version. This might be a solution for the people who don't want to buy a remote control to downgrade.
Now I tought I could try the upgrade again, and it now says "please insert appropriate disc"... I can't upgrade anymore 
I am now trying to burn it with alcohol 120% on a another verbatim and I'll see what it does.
Update:
The disc I just burned works fine so far. So I guess it was only a bad burn. There is still a little glitch where it can't route one address when punched in the "search by address" but can route when I grab that same adress from the favorites. I guess that burn is still not perfect, I'll buy sony +R DL discs and try to burn it at 1X speed, for some odd reason Alcohol 120% was only burning at 2.4X without any other option. Maybe because it's the trial version. The crack for it did'nt want to work on vista looks like.
Anyway, thanks for posting that update!