Do Planeswalker's have summoning sickness, or can you use one of their abilities the turn it comes into play? I looked over the Comprehensive Rules and saw nothing that would say one or the other.
Here's the rule:
212.3f A creature's activated ability with the tap symbol or the untap symbol in its activation cost can't be played unless the creature has been under its controller's control since the start of his or her most recent turn. A creature can't attack unless it has been under its controller's control since the start of his or her most recent turn. This rule is informally called the "summoning sickness" rule. Ignore this rule for creatures with haste (see rule 502.5).
A planeswalker is not a creature, and its activated abilities don't have the tap symbol or untap symbol in their cost, so the summoning sickness rule doesn't apply. You can play a planeswalker's ability right away.
How about on the end step? Say you have a Gideon that was bounced by Venser? Can Gideon still +2 on the end step?
Loyalty abilities can only be activated anytime you could cast a sorcery, which is during either main phase, when you have priority and the stack is empty. You will not be able to activate it during the end step.