network with same account.

So
I code in asp.net and i have my membership classes ready and done.

so i was thinking the following

if i were to make a network of sites, is it a good idea to use the same database?

so users can register on my betting site, and play. but then they can head over to the image upload, and create a gallery. while on the image upload site, they can also upload an image that will be their avatar for the whole network.

then they can head over to the arcade site, and with something manipulating (some thinking required), they can use the credits earned from the betting site at the arcade site.

then they can go to a discussion forum,and again sign in with there account and start posting.

good idea?