Are there anyone out there that ran multiple webapps with each their own database but with shared WebAppUser and/or WebAppSession tables?

Are there any foreseeable problems with that?

Would it mean that if a browser hooked up to two different such systems (on the same web-server obviously) could actually share the same session? And thus logging in between webapp switches is unnecessary?

In general, what do you do if a customer has a multitude of webapps but wants one user database?

To sum it up: ????? :-)