Looking at these brand-new iMacs, the cheapest model, with applecare (a silent gotcha, it would be foolish to purchase a machine without it)...
$1468
That $1468 gets you a machine with a mediocre display (and glossy whether you like it or not), a less-than-mediocre graphics card, as small a hard drive as you will find nowadays, a mediocre cpu... and about all you can upgrade at a reasonable cost is the RAM, from third-party sources.
The iMac line starts as a rip-off on the unwary consumer, and only gets more expensive as you go up the line.
By the time you reach the "decent machine" configs, you are easily over $2000.
I will skip the top-of-the-line 3.06 model for consideration, because of course the customer gets dinged extra hard there.
Nope, let's just take the stock 24" 2.8 model, add the silent rip-off of $169 to have a warranty that lasts three years, add what is currently above average (if that) in a graphics card (although it will be average at best during the lifetime of this current model)...
And here's the kicker: because the hard drive is such a pain in the neck to replace, you really want to lock yourself into a big one from the start; or else, deal with firewire extensions forever. So let's go ahead and make that a 750GB drive (the 1TB is such a rip-off, that I cannot bring myself to consider it).
Total: $2268
That is just a ridiculous price tag, specially since, for that kind of money, one would expect a non-glossy display (at least as an option!).
For $2268, you are stuck at a mediocre-to-slightly-above-mediocre hardware tech level for the consumer market in mid-2008. With a glossy display. With no chance to upgrade at a reasonable cost.
You will, of course, want to put the max of RAM on this machine, which third-party sources will provide for you at around $100. But that's it; if, at some point during this machine's (hopefully long) lifetime, you decide that 4GB is just a little tight, well, sorry, that's all you can do there.
$1468 for the least expensive option: a premium price for below-average hardware. An out-and-out rip-off which will only get worse as the months go on and the configuration ages.
$2268 for the more expensive option: an extra-premium price for average-to-slightly-above average hardware. That is pretty much a rip-off, although if $2268 is within your budget for a computer, then perhaps you are expected to be casual about repeating the same expenditure in a couple of years when your machine is clearly lagging in specs behind the current models.
As of today, the only Apple desktop computer that is a good purchase is the top-of-the-line, circa $3000 Mac Pro; the iMac is somewhere between an out-and-out rip-off for the least expensive option, to pretty much a rip-off towards the more expensive options.
A couple of years more like this and only the well-moneyed clueless will keep buying these things. A couple of years like this and only the hackintosh clones will keep OSX from becoming an incestuos little OS.
A couple of years more like this, and anybody with a brain for computers will either be running a legacy Mac, a hackintosh or that year's Ubuntu.
This year, I went for a Mac Pro. It fits some of my needs, but unfortunately one of my needs is to be able to peer with other people computer-wise, and at the moment I'm only able to peer with the ones that are rich enough to buy these expensive machines, or who bought apple machines in previous years (when they were a good deal).
I cannot currently recommend such a purchase except for a Mac Pro.
This time around, I gave the linux option a good hard look, and chose to pass. Three years from now, it'll probably be a good time to make a pretty permanent switch.