Spup,
I finished the wedding less than two months ago, so I hope the following is helpful.
-- If you already have it, then maybe you really don't need it again.
My wife and I had some disagreements about this, but I was of the opinion that if we had something already and it worked as well as originally intended, we didn't need a new one just for the sake of having something shinier.
-- We wound up returning quite a few things that we registered for. When we originally did the list, it was fun to keep adding things to the list. But now, we realize that we're never going to use the bamboo vegetable steamer. Or the zester. My wife also registered for a lot of cute -- her word, not mine -- throw pillows from Pottery Barn. They went back, largely because the ones we already had are fine.
Keeping the list streamlined to things you actually need helps in one other area -- receiving my favorite gift, cash.
If your registry is fully purchased, then people will be left with little choice but to simply write a check. We did quite nicely in this area. Of course, you do run the risk of people then finding some random candlestick/serving dish/decorative piece and sending that.
-- Put items on that give people a price range, but only to an extent.
Not to sound greedy, but set the bar fairly high. If you've got a bunch of $20 gifts, then the people looking for your most inexpensive item will get those. If your most inexpensive item is $40, then people will be moved toward getting those. Also, don't be afraid to put something very expensive on your list.
We threw on a furniture piece from Crate and Barrel, never expecting it to be bought. Lo and behold... At the very least, you get a 10 percent discount at C&B off things from your registry for a year after your wedding. So if you have an expensive item that no one buys, you would get 10 percent off that if you chose to get it yourself later.
-- We registered at Crate and Barrel, Pottery Barn and REI. We got a lot of our camping stuff off that last registry, which was a lot of fun.
-- Stick with the basics, and you'll be fine. Cookware. Glassware. Sheets and linens. Dishes. We added a top-of-the-line blender and food processor to those, and we use them on a daily basis.