Ha, 'remember it' he says - it is one of those things that get *etched* in the memory with 'extreme prejudice'
To Pille, the question of how to handle Wraithgates has never been formally resolved. Essentially there are three ways that have been mooted / played over the years
- Wraithgates may never be blocked.
This means that the entire Eldar formation can exit the 'gate, though they must engage the formation whose ZoC they have entered. - Wraithgates may be partially blocked.
The Eldar may only exit enough units to move into B-B with the enemy unit that is located on the 'gate (typically 2, unless the enemy unit is a WE.). - Wraithgates may be completely blocked by the enemy.
No Eldar formation may exit the gate while there is an enemy unit located on the 'gate.
Over the years we have tended to play either option #1 or #3 (discussed in the 5 min warm-up), however in practice they tend to end up meaning the same thing if the enemy manages to get a powerfull formation positioned with it's ZoC covering the wraithgate. The moral of the story is to try to ensure either that you have alternatives (Storm Serpents), or that the gate is not easily accessible to the enemy (use the Blitz).
Note, you need to be carefull over movement of Eldar units within the enemy ZoC, which governs the direction that Eldar units can exit the 'gate and remains in force until one Eldar unit gets into B-B with the enemy unit in question.
Also note that the Storm Serpents' wraithgate can never be blocked and still operates even if it is broken. They are relatively fragile 'bullet magnets' so need to be used carefully, and the presence of the Eldar Autarch on the battlefield becomes a must (for his re-roll).
After a quick search, so all Eldar Lists include a Gate ? What about Exodites ? 
I'm old ... 
Based on the fluff, these backwater rustics of the Eldar race probably wouldn't have a gate ... 