Well, the easiest would be to have two tables: One for the users and one for the subscriptions. The users table would hold the general information about the user (unique ID, email address, name, username, password-hash, etc.) and the subscriptions table would hold all the subscriptions links along with the user-id that it's linked to. So some sample tables:
-- Table: Users
id | username | password | name | email |
1 | bpat1434 | c132m1n1n1n6n191n0anz08anz81n491 | Brett | user@domain.tld |
2 | STyL3 | 1na8nznb8018tnt810z9an10q0r9tgw0 | Style | user2@domin.tld |
-- Table: Subscriptions
id | userID | link
1 | 2 | http://www.phpbuilder.com/board
2 | 2 | http://www.php.net
3 | 2 | http://www.mysql.com
4 | 1 | http://www.simplemachines.org
5 | 1 | http://www.phpbb.com
6 | 2 | http://www.somesite.org
Then when you query the tables, you can get subscriptions by limiting the userID. You can also easily add, modify, and remove subscriptions per-user. Much easier to handle the data returned.
Hope that gets you started in the right direction.