One. This laptop I am typing on right now. It's got 1GB RAM, 120GB HDD, and I forget any other specs. It's dual booting Windows XP and Slackware Linux; I use Linux for just about everything, but if for some reason I need to boot into windows for something (rare), I will keep windows.
Then I have few blade centers , a bunch of rs6000's two I-series a dozen of X-series here also I am not counting all the pcs and laptops my organization have.....
No. Don't count devices at work...... unless you work at your home.
OK, your turn matrixmadhan,.... time for your poll 
yeah still using one good old pII-333 ... with linux (of course)
Will move to a better (and secure) one soon 
3 x86 pc (Intel Celeron, Intel Dual core and AMD sempron -w-~ 1.5 gb RAM apiece),
serving as home network infrastructure and one doing dbl duty as primary workstation. Two newer laptops that are used occasionally.
Powered On:
Game PC
Wifey PC
Laptop
ultra10 running netbsd
I will try not to think about the parts/powered down abomination in the garage. It ranges from a PET to a relatively new hp Bclass.
One. This desktop I am typing on right now. It's dual booting Windows XP and Solaris 11.
I have 6 total at the moment, I am preparing to shutdown the Ultra1 and the Octane soon though and just use the xeon based Mandrake box. As soon as I pick up a PCI SCSI card for the raid box. I will hate to see them go, but you have to let go of the past at some point.
1 desktop (Vista)
1 desktop (XP)
1 laptop (XP)
1 desktop (Mandrake)
1 Ultra1 (Solaris 9)
1 SGI Octane2 (Irix 6.5.27)
Since APs and such are not counted, even if they're running something like OpenWrt I must settle on 4.
I wonder if one should count game consoles? I've got an xbox that's on the network...
My count came to over 5 without it though so it wouldn't scew my answer anyways 
Quite a shock actually, I thought I had very few but there's the media centre PC, sun server, laptop running XP to provide network console access to it, another XP laptop and desktop, another XP laptop to handle queued file downloads etc (always on, always busy). Business laptop is home and used most evenings, If I'm on call my work laptop is home too. Then there's the xbox.
Loads more in bits of course 
So that's 8 or (9 if you count the xbox). Would be 9 (or 10) but my fileserver is broken at the moment so doesn't count (around 9 drives too close together and relying on convection to keep it cool = pretty bad idea in hindsight).
Yeesh.
Love the SGI hardware, not so hot on IRIX 
My old Indigo2 is still sitting under my desk - not been switched on in years... Poor neglected thing.
I also have an Indigo, O2, and a Octane. All sitting in the corner wishing they were usefull again. I am thinking of doing a casemod with one of them.
Gads ... A twin pair of nice, custom, Fedora 8 desktop boxes for me and my lady, an scsi ultra 160 based postfix box, a klunker 700 Mhz IPCop/Copfilter box, a good test box with dual 1000 Mhz P3's and onboard U160 support, and an ancient IBM PS/2 77S box with a couple of scsi external full height drives that acts as a file server of sorts. I refuse to get rid of the PS/2. I actually started with an old XT dual soft floppy box but I grew up on the PS/2. All boxes are generic self-builts except the PS/2. I guess all that counts as six. I just junked a worn out/burned out HP Pav. 6736 that used to be the firewall box. There are also several running P2 & P3 klunkers in the closet. I recently gifted out a couple more.
Hmmm....
My electronic thermostat has more computing power than the computer they had on the Apollo 11 lunar lander . . . and it DOES generate heat . . .
Nah. I counted my laptop and the wife's desktop.
Only one!!!! - (not considering my Office PC)
My lenovo Y410 laptop using cygwin
3 PC
2 macs
2 HP (715 & B180)
1 HP D270
1 SUN sunblade100
Four at the moment.
24" Imac
1 pc Mandriva 2008
1 pc Windows XP
1 pc Windows 2000
9 computers here.
2 PowerBooks (1.25ghz and 500mhz)
2 iBooks (300mhz and 500mhz)
Mini (1.83ghz) with 2TB of firewire storage
Dell gx270 (2.8ghz)
iWill SFF (1.7ghz)
beige box (1.4ghz)
beige box (dual 1.7ghz)
You use them all regularly?