The way I see it, you owe a good server a good tip. They shouldn't be penalized because the establishment runs a special. I say, "Tip the special!" Here is what I mean using an example from today:

I walked over to Brewdawgz, which is a .7 mle walk from my camper, the Colby T. I walk it so I can drink some beers with (or without ) my meal and get back to camp without breaking any driving laws. They have great draft beer there, and I can't always leave with only one or two.

Tonight, they had Old Courthouse Ale on draft for only $1.50. I had three of them. I would have done, even if they were full price. I ate a Brew Burger. My bill came to $15.68 with tax. My usual tip on that would have been $3.00, because I always leave 20%. That would have been unfair to the server.

A beer at Hills and Dales would have cost me $4.50. Today, I drank three for $4.50, saving me $9.00. But, by tipping the special, both the server and I benefitted. Here's how: I left a $10.00 tip. That made my total about $25.00. The server got close to $5.00 extra. I still saved $5.00 over what I would have paid at full price- It would have been about $26.00 with tax + $5.20 for a 20% tip = $31.20.

Case proved. Don't be a cheapskate. Tip the discount!