Can't seem to do this for some reason.
I download the *.gbx files and select Open with Mania Planet executable but nothing happens...
Any pointers or ideas? Cheers.

same problem here, and also everybody has this problem.
I think that isn't possible to open gbx files yet...
This problem has been already posted on maniaplanet forum

sam here. no answers on MP yet (posted by me btw^^).

Probably because .gbx files are specific to TM2
ManiaPlanet will act as a hub for all 3 games (TM2, ShootMania, QuestMania), so eventually when we click to play ManiaPlanet there will be an option to choose which game you want to play.
So when we try to open .gbx files in ManiaPlanet it doesn't know what to do.
Hopefully at some point Nadeo will add some code to tell it what to do with each file designation.

so atm MX is almost unusable, since we can't just open the file. we need to:
1) save it;
2) open maniaplanet;
3) go to local->select map.
-.-

No MX is not unuseable
You just have to play the file in game, like you said... not really that hard. If you do find that hard it might be worth walking away from PC gaming and having a think about trying out a console. The 360 is really quite good.
Surely you don't just download one file at a time and play straight away then close the game to download another?

Not sure if you guys know this but you can specify the location to which you download a file. Download the track files to your tracks directory and its super simple to find them ingame. Doesn't take much to manually organise that folder either.

I don't wanna go to console, I just wanna TM... for fun counted how many clicks do you need:
with TMUF: 1. click on DL link 2. click OK => success
with MP: 1.click on DL link 2. click OK 3. click Save 4. click MP launching icon 5. click Play 6. click Local 7. click Single map 8. click Downloaded (folder) 9.10. select the map (averagely, usually the track is not on 1st page) 11. click Play => success

^^
yep, I'm that lazy xD

I admit I also miss the feature from TMF, just rightclicking the download button of the track and then choosing "open with tmforever" , it made it really easy to test a lot of maps on tmx and then award/comment them.
With TM2/Maniaplanet, I find myself testing less maps, because it is more complicated.
I think less known authors would benefit the most, if .gbx files could be directly opened with Maniaplanet/TM2.

Space says:
I don't wanna go to console, I just wanna TM... for fun counted how many clicks do you need:
with TMUF: 1. click on DL link 2. click OK => success
with MP: 1.click on DL link 2. click OK 3. click Save 4. click MP launching icon 5. click Play 6. click Local 7. click Single map 8. click Downloaded (folder) 9.10. select the map (averagely, usually the track is not on 1st page) 11. click Play => success

^^
yep, I'm that lazy xD

jeez, you're so lazy you don't want to click eleven times to race on a track, but still you had enough time to waste counting how many clicks you need to do it. take it easy pal, but that's just nonsense to me.

Man, this is not nosense...
If you would have been a bit active on tmx, you should know that to test maps, is really annoying to download them, open your downloads folder, select them all, and put them in the right tm folder. And +, you have to close and reopen the game, because the refresh button inside the game, if you added too many maps, makes the game crash.

So, that gbx thingy is annoying me a lot too!
Is a 1/10 that would help mx to bring more activity!