Grim Batol is part of the Misery Battlegroup which consists of 14 English-speaking realms.
It has been confirmed by a Blizzard employee that Grim Batol is the most populated European realm, however, recent free migration may have changed that. As a result Grim Batol is listed as "Full" on the Realm Status page and migration to Grim Batol is locked.
The Horde to Alliance ratio is pretty even, around about 40:60, most players do not believe there is much imbalance during their day-to-day play.
As of Wrath of the Lich King release the server was experiencing queues of up to 800 on weekdays and considerably higher during weekends but now they are gone.
Grim Batol is populated by players of many different nationalities from all around Europe. Since there are so many different nationalities, it is advised to speak English as it is the most commonly understood language.