I own a 2007 model 24" iMac. (I live in Oz)
It has done 2 hard years of work for me, I had a noisy optical drive replaced under warranty.
I dual boot OS X & Arch Linux. I prefer Arch to OS X, as it allows me near total control of my setup, whereas OS X has many limitations in that regard.
I wrote an installation how-to which is on the Arch wiki, you probably won't be interested in it, but I'll post the link anyway:
http://wiki.archlinux.org/index.php/IMac_Aluminium
Good luck with you iMac. They do cost a little more (probably depends on where in the world you are as to how much more), though they are incredibly space efficient, & the display quality is great.
I recently upgraded my 320GB HDD to a 1.5TB WD Green HDD, cloning it (file systems were fat32, HFS+, Ext3, JFS) with Clonezilla. Not a problem. If you ever need to get inside of your iMac give me a yell & I'll tell you what I know.
