Is CodeIgniter Suitable for every Application?

[eluser]newbie22[/eluser]
I have read a little about CodeIgniter but not yet convinced the benefits apply to the website I intend to build.

I want to build an International Trading website that will involve numerous databases from which users will be able to interact. In the commencement of the User Guide it refers to a website for the publishing news items which is quite different to the site I intend building.

I am at present focusing on a registration/login script and the User Guide appears not to facilitate that type of start to a website.

Can somebody please provide some advise?