I upgraded to Lion recently, to take advantage of the new iBooks Author (iBA). I have to admit that I find nothing compelling about either of them, really. Lion offers no compelling advantage over Snow Leopard that I can see -- except that Apple seems to be making some programs available only on Lion (although, in the case of iBA, I can see no technical or functional reason for doing so).
Worse, some of the most exciting features of Lion, like Lauchpad, are inherently broken and are unusable. The operating system takes enormous liberties with file permissions, locking files without explicit instruction and then forcing you to create duplicates in order to save without overwriting the locked originals. Scrolling out of the box is backwards, and scrollbars are missing. If you buy Lion, I hope you've got time to spend de-lousing the system of all its fundamental flaws.
I've been using Macs since Tiger, and this is the first product to come out of Cupertino with which I haven't been thoroughly pleased. If I didn't need iBA, I'd go back to Snow Leopard in a New York minute.
On a scale relative to Windows, Lion is yet another competent Apple release. On a scale relative to other Apple products, Lion falls very far. It's like they pushed it out before it was ready, with features that were shoehorned in just because somebody thought they were cool, and interface changes that improve the user experience not at all. They should have titled it OSX 10.7: Vista.