@ Halfling Barbarian
I think he means acrobatics check, not balance check. 3.x terms still tripping us up from time to time.
@ Maezer
The disk forms in air. It does not, as far as I can tell, rise up from the ground and pick up whatever was there. The archer would need to spend a move action to climb aboard, but that is not a big deal, as the spell lasts for hour/lvl.
Also, for those saying it needs to be 5ft away, that was 3.x as well, it can now be directed to move away or hold position. It only winks out if the caster goes beyond short range away from the disk.
As the caster also probably wants to stay out of melee, same as the archer, this is simply providing action economy to the archer in the event that both need to move away from advancing enemies. It is situationally usefull with no real investment on the casters part, aside from maybe the spell slot to cast it.
Lastly unless your talking about halflings and gnomes, this is at least a second level tactic. Most other races are to heavy to be held at first level by the disk. Actually I would say this is at least a 6th level tactic, since the archer doesn't truly need full round attacks until he gets more than one attack anyway.