2 iPhones, currently same Apple ID, ramifications, how update?

both my spouse and I have the same Apple ID on our two iPhones. this has never been an issue and was done as at the time as nobody told us otherwise.

however, I'm now interested in upgrading my iPhone 3G to the 4S and she will be doing same or at least upgradeing her iPhone to the latest iOS 5, she currently is at 4.1

will this be a problem that we both have same Apple ID for the iCloud or any other reasons? such as when I go to download apps I've bought before, which I believe is now something that iOS 5 will let us do.

is that something both of us will have access to? will it be a problem if both useing same iCloud? should the person who as bought far more apps keep the ID and the other get a new one? will that wipe out apps already on their iPhone? I've also heard that we can use a seperate Apple ID for iCloud and for purchases.

I'm not even sure if I'm asking this correctly as not sure of all the ramifications here. such as another issue that I'm curious about here, is what happens to contacts? may we share one contact set on desktop Macintosh and both synch to same iTunes and or iCloud?, or is everything seperate now with iCloud?

it is preferred that we do share same contacts and just deploy as needed with a group, the contacts we each need to our individual iPhones