All in One or Desktop PCs?

Clarifications

Apple make a desktop All in 1 Unit that seems reliable within the limits of it's design or if you mean a Note Book or Net Book which tend to be more fragile and less reliable than a desktop, not to mention piratically impossible to upgrade in any meaningful manner.

Col

hardware upgrades on, while the traditional desktops allow for easy component upgrade. The one thing that's kept me from considering an all in one like the Apple Mac or the newer NEC ones is you're locked into a specific monitor size and resolution for the entire lifespan of the device, and since I usually run several years to a device, I like to be able to upgrade the monitor as I see fit. My current system came with a 17 standard square type inch and now sports a nice 23 inch wide screen. Also the all in ones do not usually play well with kvms if you wish to sue one for any reason.

Schools use Mac and HP all in ones all the time. If you really want to test something's durability, set it in front of a bored 8th grader. They hold up very well.

If you are in the 90% who never open the case, upgradeability is not an issue. Although, you may want to ask how and with what you would replace the DVD drive.

Are you a modder or willing to leave well enough alone? I run an onsite PC support franchise and repairing a dead disk drive in a standard desktop would take my techs less than 20 minutes. In an AIO, replacing the hard drive is two hours.Even faster for an optical drive. So if I were buying new, I would be inclined to get the extra warranty coverage on an AIO whereas I wouldn't bother on a desktop.
All else being equal, I would choose the desktop but that's me.