Raiding in WoTLK will bring some new options to the table
First of all, all raid instances can be done in either a 10 man form or a 25 man form. Which creates lots of opportunity for social guild who like to raid and make some progress like ourselves.
But why would anyone do a 25 man raid when you can do a 10 man raid of the same instance? Basically the difference will be the same with the burning crusade dungeons on normal and heroic mode. The 25 man raid (or the Heroic raid) gives better loot. For example; 10 man Naxx drops T7 loot where the heroic version drops 7.5. Wait, did you say T7.5? Yes i did. The looks will be completely the same only the bonusses on the 25 man version will be slightly better. Compare Heroes' Scourgeborne Battleplate which drops in the 10 man version with Valorous Scourgeborne Battleplate which drops in the 25 man version.
But epics aren't the only difference in drops. As in TBC heroics and raids will drop badges but with slightly alteration: the 5 man heroics and 10 man raids drop 1 kind of badge (emblem of heroism) while the 25 man (heroic) raid drops another kind (emblem of valor). What will be the difference in rewards is unsure right now.
To be clear: You don't have to do 25 man raid to progress, although it will surely help because of the better loot, a guild could only do 10 mans all the way up to Arthas. And also doing a 10 man version of the raid doesn't save you for the 25 man. The same is true for the other way around. There will be no attunements for the heroics 5 mans though some raids will require a drop from a previous raid boss (1 person in the raid needs it).
Currently we've limited openings for all classes, all specs. We expect applicants to stick by us as we make the transition into Cataclysm in a little while!
You might also consider becoming a guild friend.