I think taglines are a holdover from the old world. The value in some of them is undeniable (e.g. "Just do it."), but generally? Meh.
With great effort I'm sure I could recall some others. If you gave me a list of major company's taglines I'm sure I could match them to the company name. But who really cares? I don't see that having a direct effect on sales.
If you're advertising in a formal context you need a proposition (e.g. "Great quality, even better prices."), but I don't like the idea of tying that to your brand name every single time it is mentioned.
The important thing is, what do I think of when I hear the name "Ford"? What does "Reebok" mean to me? et cetera. In other words, brand perception. A tagline is certainly
one way to shape that, and in that sense it can be a useful tool. But it's only one way, and I don't see it as a
necessary tool.
I think many companies need to be reminded of that important principle in writing:
show, don't tell.
A tagline is meaningless if it's not backed up by your brand. If your brand already embodies your idea, then articulating it is at best unnecessary, and at worst trite. There is a mid-ground, but I don't think many brands need to occupy it.