If people are still using Photoshop to design logos thats a bit worrying. Illustrator creates far superior logos than Photoshop. Granted if you want an effects heavy logo it wouldn't really go as well in Illustrator but having a Vector based logo is far better in the grand scheme of things than a Rastor logo. Anyway, On topic here; http://webflake.sx/topic/4699-suggested-format-for-logo-requests/ - Use the format.