Apple this week upgraded its desktop line, boosting the speed and power of its Mac Mini, iMac, and Mac Pro. The Mini is once again a nice low-end system for someone looking for a second Mac. The company added even more power to the Mac Pro, its high-end desktop for people who need a lot of power and are willing to spend a lot of money for it. That leaves the all-in-one iMac stuck in the middle. In an era when desktop PC sales are being eroded by netbooks, notebook computers, and the floundering economy, how long will the iMac survive?The announcements injected new life into a desktop line that was aging across the board. The new 24-inch iMac has a 2.66-GHz Intel Core 2 Duo processor, 3 GB of DDR3 memory, a 640-GB hard drive, and Nvidia GeForce 9400M integrated graphics, priced at $1,499, same as one of the older 20-inch Macs. Pricing starts at $1,199 for a 20-inch model.

The Mac Mini gets new graphics, and the GeForce 9400M, for a fivefold improvement in graphics performance, and improved energy efficiency. Pricing starts at $599.

Apple cut the Mac Pro starting price by $300, to $2,499, upgrading the processor and internal system architecture for up to twice the performance of the previous generation. The new Pros include Nvidia GeForce GT 120 graphics card as as a standard, for triple the graphics performance over the previous generation of Mac Pro. The graphics upgrade will make the machine more appealing to scientists and videographers, said Ezra Gottheil, an analyst with Technology Business Research.

John Gruber, writing on the blog Daring Fireball, summed up: "$1,499 now gets you a 24-inch iMac, and the $1,199 20-inch iMac now has twice the RAM and storage. The entry-level Mac Pro is $300 cheaper, at $2,499."

The upgrades come at a tough time for Macs. While Mac sales outpaced Windows PCs for months, January saw the reverse. Mac sales fell 6% in units sold year-over-year, and 11% in revenue. Windows PC sales, on the other hand, were up 13% in units, while revenue was flat.

The news is only going to get worse. PC sales will decline this year by a whopping 12%, the steepest drop ever, according to Gartner. The previous worst year saw a 3% decline in 2001.

The bad news is likely to hit iMac sales particularly hard.

Mac Pros will do all right; they've always been a niche product for people who need a lot of power and flexibility.

The Mini is a nice little workhorse of a machine. (Should we call it a "work-pony"?) Larry Dignan, writing at the ZDNet Between the Lines blog, asks: ">"Is the Mac mini irrelevant?" and his readers respond, "Heck, no." It's not a sexy device, but it's handy: You can cluster them to use as server farm, rack them to provide computing power for audiophiles, or use them as a cheap desktop for people who already have their own monitors, keyboards, and mice. You also see them in use as point-of-sale systems.

That leaves the iMac as a midrange, all-in-one desktop. But consumers are losing interest in desktops. Midrange users are more likely to turn to notebooks; while PC shipments will see a double-digit decline this year, mobile PCs will grow 9%, says Gartner, fueled mostly by increased demand for netbooks, but with demand for full-sized notebooks also increasing. People looking for a midrange Mac will likely avoid the iMac in favor of a PowerBook.

We may well be looking at the last generation of iMacs -- ever.

I'll be sorry to see them go. The iMac was a driver for Apple's comeback; the candy-colored iMac, launched in 1998, was the first machine introduced by Jobs when he returned to the company. And the iMac has personal significance for me; when I switched from Windows to the Mac two years ago this month, I bought a 24-inch iMac, and it's still my main machine for work and play today. But sentiment is no reason to keep a failing product line alive, and I don't think the iMac will survive the recession.