Thanks for the explanations about all the OVI stuff, I belive I did not erase anything at all for now because each time I made the command:
apt-get remove "package"
it responded me nothing which seems abnormal,

it's the same when I do apt-get update or install
it's getting a problem as I need to install some stuff that way and I would prefer to use the good old apt-get to install stuff.

Do you have any infos ?

PS: I did the command with sudo and in a root shell (with sudo gainroot typed before).

Thanks in advance

@endsormeans: ok, I'll test the OVI maps stuff but it'll be the only one I will keep (if I do), I tested marble on the N900, it did not convinced me but it was on a tv and I had no image on LCD (the precedent N900 I had was damaged) but I use marble on my desktop/laptop and it does a great job for my uses (essentially marking points on a map and a bit of routing).

@Pichlo: it's now too late but I will remove cherry as soon as possible and I did not sign or fill anything but the little contract with the welcome screen.
@peterleinchen: sadly, it's too late now, I signed because I knew/thought a lot of that stuff was not working anymore, anyway, what will this imply to me ?

Also, I heard that the N900 was a bit lacking of autonomy however since I charged the battery, now it's working since yesterday without charging (altghough I used it intensively 4hours with wifi and or bluetooth and made 5-6 calls, ...) and the battery is still almost full (3 pixels down (I checked with my camera zooming on LCD)), is this normal ?

I really need to solve the sudo/apt problems so that I can make my phone better because for the moment, I can't watch 720p vids, connect to a DLNA/UPnP device with mplayer or an alternative file explorer, watch online videos, ...
and it will be important for me to have those functionalities, also I'll try to enable the USB host mode and also mumble, gqrx+my sdr dongle and some way of streaming the camera.
However before being able to try all of that, I need apt working fine, if possible like on my desktop

Thanks in advance guys, you are helping me a lot