In regards to corkage, I find that $5-10 is totally reasonable, $15 is OK, $20 is getting a bit steep, and anything above $25 is bordering on extortion, save being in some of the finest restaurants.

I bring my own wine because I know it's ready to drink, it's what I like, and I know how it has been cellared. I can open and decant a bottle at home for several hours, return to the bottle, re-cork, and bring to dinner. This way, it's had plenty of air-time, and is immediately ready to drink.

I always offer a taste to the waiter and/or som. I often buy a bottle off of their list, generally a white or dessert. These motions usually get corkage waived. I also tip very well when service is great - the waived corkage charge often goes to the waitstaff.

I realize that the restaurant is doing me a favor by allowing me to bring in my own wine, and I respect this. I am also doing a favor to them by offering them my custom. It's a two way streeet. I always check the list to make sure that I'm not bringing a bottle in that they have on their list.