I was watching a SethBling video and he was reviewing snapshot 13w39a it turns out they add command block minecarts (ID:422) so I used the command block minecarts to summon primed TNT rapidly 20 blocks above and I came up with a cloud you can jump on.

it is now compatible with the latest snapshot I did just a little change so that it still bounces you straight in the air as normal

you can now use this for your own adventure map because to me its useless :D

Additional Notes

must be playing in snapshot 13w39a and over for this to work also don't place this where you want your cloud to be, place it on the ground and the TNT will be summoned 20 blocks above and you have your cloud.

sorry if this explanation isn't so good.

also if you don't know how to place a schematic into minecraft it requires MCEdit and heres a tutorial

http://www.planetminecraft.com/blog/how-to-create-a-schematic-in-mcedit/