As a loyal customer for almost 10 years now, I'm not really interested in a loyalty discount, I won't phone up PlusNet demanding a MAC in the hope I get 20% discount applied to my account for the next 6 months and Keira Knightly as my personal maid, ok, maybe if you could offer Knightly..... I'm loyal because the service is good, the customer support is good, the forums are good, generally because (for me) PlusNet (Force9) deserves my loyalty, and I repay the good service I get by giving them their due allowance (my monthly fee).
Previously PlusNet have offered a discount for loyal customers, agree to sign up for another 12 month contract and you got 10% discount for 3 months, which I did take! If you move house and agree to an 18 month contract, they waive the fee (at least in my case they did), so they do reward loyalty in their own way.