I added asp.net membership in my web application. Now I have one table where I have columns for user specific information UserProfile(FirstName, Lastname, DisplayName etc.). I didn't use Profile from membership because if in the future I decide to change asp.net membership for something else I want to keep user personal data in separate table. My question is: I use UserId (unique identifier from asp_membership_users table) as a foreign key in my custom table. Is UserId smart choice to connect these tables?
Yes, it's the primary key of the asp_membership_users table so it makes sense to use it as the foreign key of your custom table.