As always it depends upon many variables, none of which were mentioned in the first post.
Desktop: no, unless you absolutely need some mac-only software. Build your own if possible (it is very easy and lets you pick the hardware you need for cheap). Run Linux Mint if possible (extremely easy to use, doesn't crash). Even if neither of those is possible, don't buy the mac desktop.
Cheap web-browsing laptop ($200 - $800): Mac doesn't make a laptop in this range, so the question doesn't apply. If this is what you're looking for, don't look at any $1000 laptops, including macs.
Pricier get-stuff-done laptop ($1000 - $1500): They definitely can be worth it, depending on your needs. The total hardware package is very good. It is hard to find the combination of battery life, screen, graphics, processor, light weight, thin, etc in any other laptops. However, I would again recommend running a version of Linux such as Mint unless you have a very good reason why not, and these can be somewhat trickier to install on Macbooks from what I've heard (?).
If you don't need Windows, then I think you should run Linux if at all possible, but I would still prefer the Mac OS to Windows. The hardware in Mac laptops (both the Airs and the Pros) are really good all-around combinations, but you pay for it. Lenovo Thinkpads are popular alternatives in this price and feature range (and you can usually install Linux easily).