I have the Chef'n Emulstir, which I bought after a fantastic recent cooking class on 30 minute vegetarian Mediterranean cooking at the foodie stuff store that hosted the class. I have made a dressing of balsamic vinegar, extra virgin olive oil, fresh squeezed lemon juice, Dijon mustard, finely chopped garlic and a bit of salt and pepper in it several times now. I like it a lot. It is nice to have proportions marked on the side, the suggested dressing recipes look nice, and the little plastic thingy inside works well to keep the dressing emulsified. I will say that it works better to mix the dressing first, then pour it into the Emulstir, as shaking the dressing while in it causes dressing to appear on the lid. A screw top design might fix that problem. Also, I am very careful with the little itty bitty cap thing which sits atop the spout -- once false move and it could disappear into the garbage disposal, never to be seen again. Re how long dressing keeps, I keep mine refrigerated (though I thaw it out with a hot water bath or some time on the counter before dressing a salad) and it has done fine over the week it takes to consume the dressing.

I don't know how long dressing keeps, but I usually just mix it in a bowl and make it for individual salads. If I were going to make dressing to keep, I'd just put it in a glass jar that had formerly been used for dressing. If you're good with a dremel tool and have the right attachment, you might be able to put those markings on the side. Did y'all see this popular thread? http://ask.metafilter.com/211616/Best-reusable-product-packaging

If you're the not-measuring type like me, dressing is easy! Tahini-based is basically hummus without the beans (tahini, olive oil, lemon, garlic, salt, maybe spices). I made a tasty yogurt dressing the other day that had the juice of most of an orange and its zest and ginger and a wee bit of salt.

I make ranch dressing, about 2 cups' worth at a time -- enough for 3 or 4 big salads. I just put it in the container I keep it in and mix with a whisk. What does a salad dressing maker *do* exactly?

My dressing's got buttermilk and mayonnaise in it, so I figure it's good for as long as the buttermilk and mayo containers say they're good for. But probably the longest I've kept it before finishing it is a week.

I make my own dressing in a big bowl as the first step in any salad. I just do the emulsifying with a fork if I'm lazy, with a small whisk if I'm paying attention.

Mostly I just make vinaigretts with different variations. On some rare occasions I'll make a small jar of it and it keeps for a very long time - with all that vinegar it's not particularly volatile. I'd say a month. But I usually just don't bother making it in bulk.

Even if I do have it in bulk, I always start salads the same way - dressing in the bottom of the bowl, greens on top of that and gently toss, and finally add mix-ins - as I learned in my restaurant years. Uses much less dressing (healthier) and every bite is flavored.

I keep homemade dressings for a week or so; I imagine they keep longer, but I tend to make smallish batches in wide-mouth jars (so I can whip them to a super-thick emulsion with the immersion blender).

One idea I saw on Serious Eats: make your own salad dressing bottle complete with instructions by writing the recipe (or "fill-to-here" lines) on the bottle with a permanent marker. That example used a purchased plastic squeeze bottle, but there's no reason you couldn't repurpose a well-scrubbed glass bottle.

I use permanent marker to label glass jars and bottles all the time. It's not permanent on glass; it scrubs off with a sponge. But that just means you're not stuck using one dedicated bottle (and its recipe) all the time. If you're switching over from an old bottle to a new one, you can easily copy the marks from the old bottle, or write up your current favorite, whichever you prefer.