Yeah - I think I managed to go through 3 housing groups in 2 weeks towards the end of term 1.
If you are heading for Warwick Accommodation, get your group ready a week before reservations open and reserve the house you want most at 1pm or whenever the deadline is in the first few weeks of term 2. Houses (especially in Cannon Park/Canley) get snapped up quickly with Warwick Accommodation.
Deals in term 1 generally turn sour. If you don't sign in term 1 but form a group, expect a lot of musical chairs and double dealings. If you have a couple in the group then it will probably fall apart in term 3 at the latest. Or if you actually move in you better pray they stay together.
Large mansions (8+) are rare with Warwick Accommodation, there are only 2 or 3. If you want your entire hall/corridor living together, things are often more expensive and you will probably have to go private. The up side is that the group is large enough so that any disputes won't have a detrimental impact on the overall group, and perhaps it is easier to find a replacement for any dropouts.