UserInfo has a .Profile or .UserProfile that exposes the profile, and then GetProfileProperty() and SetProfilePropery() functions to set and get them.  When you're done changing a value be sure to use the profile controller to save profile changes...  those names might be a little off, as this post is from memory..

 

I went through this same ordeal and ended up using a stored procedure on the database that I could pass the userID and the custom profile property name.

Here is the query to the db in the custom procedure.

    SELECT     dbo.UserProfile.PropertyValue
    FROM         dbo.ProfilePropertyDefinition INNER JOIN
                          dbo.UserProfile ON dbo.ProfilePropertyDefinition.PropertyDefinitionID = dbo.UserProfile.PropertyDefinitionID
    WHERE     (dbo.ProfilePropertyDefinition.PropertyName = @CustomePropertyName) AND (dbo.UserProfile.UserID = @UserID)