It's a fact of life (and of this business) that whatever you do, someone somewhere isn't going to like it.
If a company is going to give specials to certain customers for whatever reason, go for it. Just make sure that whatever special is applied consistently, so that if someone tries to raise a claim of preferential treatment (or a complaint about their *not* getting preferential treatment because of X-Y-Z) the company has the power to refute that statement.
Depending on what kind of specials/discounts you offer, and to whom, I think it can have an all-around positive impact. For example, giving a free year of hosting to customers who stay with your hosting company for five years makes you feel good - because you've had this customer and their revenue for half a decade, and may for the next half-decade - and makes them feel good - because they suddenly get to save money that they'd probably budgeted as 'spent'.
Just make sure that the discounts aren't constructed so as to seem like more of a lure than an actual discount (five years' regular patronage gets a 2% discount for one year's worth of hosting, which can be really really small on some services) or so large that they either make your company seem like they're giving away the farm -=or=- be financially ruinous to the company. There's also the possibility that if you give customers something at five years, they may think that it will be equalled in another five years' time.
I have seen plenty of places that offer discounts for new clients, but not those that offer them to existing customers which in and of itself always annoyed me.
