Hoo-boy:

1. Inspiron 6000 series --> No OS (Windows crapped out on it and I'm too lazy to get around back to it). When I feel motivated, I'll be turning it into a Linux box

2. Toshiba Tecra A9 --> Windows XP. Just retired it back in September of last year. I still keep it as a backup desktop machine if it is needed

3. HP dv7 Series --> Windows 7. My new primary desktop machine mostly being used for fun and for school work

4. Lenovo Thinkpad X200 --> Windows XP. I use this one as my primary machine while I am out in the field working at my job, and I need to do something that my company computer won't allow   me permission to do.

5. Dell Latitude E6400 (I think) --> Windows XP Proprietary Image. My work issued computer. Hate it because they don't give us permission to do anything on it and you have to file an MOC with the company any time you need to get something fixed or add software. I keep it just because I don't feel like giving it back and because there are 1-2 odd jobs I have to do that can only be done by logging into the company remote access network and that can only be done through the company computers.

6. Acer Aspire 1 --> Jolicloud. I bought it a couple of years ago, never cared for it and gave it to my mom because she liked the size. She ignored after we got her a nicer machine and so I re-commissioned it as a test platform for trying out the Jolicloud OS (which actually, is kinda nice)

7. Sony P-Series netbook --> Acquired this a couple of weeks ago. My dad bought it right after I got the Acer and hates it because he can't deal with the small size. Since he just got a new machine that he was ogling while we were in Korea, he tossed it in a drawer, and I stole it to play around with.

Only one.
 

HP Elitebook 6930p (T9400, 3gb, 500gb, hd3450, Vista). Used for everyday use: audio storage, work, light gaming, photo edition, etc. It's been reliable up to now and the matte 14" 1440/900 screen is something I dread losing if I switch to a newer computer (I hate the 16/9 ratio).

Having one computer of my own is more than enough when I've also to care for 36 computers of various ages abused by a bunch of computer illiterates.

Samsung N150 Red - Atom 1.66 GHz - 10.1″ - 2 GB Ram - 250 GB HDD    Windows 7 Netbook

Sony VAIO T4200 2.0 GHz   64bit Windows Vista Laptop  

Macbook

1 Samsung Netbook

1 Sony Laptop

1 Macbook

2X post sorry

Quite a few...

I stopped with the addiction of upgrading my main desktop every year only because I stopped playing games. I even removed my expensive video card to save electricity!

Here is what I have now:

This one is a few years old and gets the job done. Built it myself of course:

2.4ghz Q6660 quad core (overclocked to 3ghz)

4gb DDR2

2TB Raid 1 for backup/storage (internal)

1TB for main drive. 7200rpm Seagate.

2x 500gb Laptop hard drives in external Raid 1 (Yes, really. Had these laying around anyway!)

2TB WD esata drive external

500gb Seagate external

... OK let's just say I collect hard drives and am obsessive about backing up my data!

Laptop #1:

Ibook G4

1.2ghz

320gb hd drive (this took me THREE hours to install. I had to remove the motherboard)

1gb ram

I never use this, but it's a good netbook alternative. I had Ubuntu on it, but very little software would run on the PPC Linux version.

I sometimes use this as a music computer with a DAC. My Nuforce Mobile even works in Ubuntu Linux! No driver needed.

Main laptop:

HP Core 2 Duo 1.5ghz

2gb ram

320gb hard drive

17" crappy display

Geforce 8400

Back when I bought this it had everything I could ever want. Now it's a bit outdated, but I don't do anything important on it. Back in the day I could even run games on it because it had a Geforce video chipset. Now it can't even run Fallout 3 until I upgrade the processor. I actually remember playing Final Fantasy XI with it quite well.

What's cool is that it has 2 hard drive slots, but I haven't felt the need to upgrade them or add more ram. I did put Windows 7 on it and upgraded to the HD to a 7200rpm drive.

I also have a PPC Mac Mini. I bought it for my mom and she never used it so I exchanged a PC for it. I think this Mac Mini is so old it's nearly worthless. Firefox on it with flash is unbearably slow. Processor is about 1.2ghz. Only 1 GB of ram. Leopard is on it and that's why it's so slow I think. It came with Tiger. Ubuntu seems to make it run a lot better. There is no flash support for PPC Linux with Firefox. That stinks. This means no Youtube. oh darn.

Just a core i5 macbook pro. 

HP DV6 with an i7 and a cheap gateway netbook

My current computer has been more or less intact for about 2 or 3 years which is a world record for me since it´s used for games and I am picky. I did ruin the run by getting a GTX 580 as of late though.

Watercooling setup run by Swiftech gear and uses an external triple fan radiator. Noise levels was not primarily concern back then which I have to eat up a bit now ;). But then again I can even max Crysis 2 running stereo3D out of it.

Cooler master Stacker case. The original model

Silverstone Zeus 850W PSU

Intel core 2 Duo 2.4 gig running at 3,6 gig.

Asus Commando mainboard

4x1GB teamgroup extreme DDR 2 memory. Since getting the GTX 580 I can only boot windows reliable with 2 gig though. It´s stable once I get it to boot but restarting 15 times is not good for my blood pressure. Suspect mainboard is going or if I am lucky it´s just the battery.

Zotac GTX 580 video card.

Soundblaster X-fi Elite Pro video card just about exclusively used as transport these days.

Displays is a 3 year old Sony KDL32V200 LCD TV. Known as XBR1 in the US. Also has a new BenQ G2400W primarily used for 3D movies, or games where input lag is intolerable and the smoothness of 120hz is preferrable.

Lenovo T61 14.1 inch laptop...had it for like 3 years so far

HP (of some sort) desktop...its basically my media center for music, dvd player, etc...as its monitor is my 32" LCD tv.

cam

I have only one 13 inch. Macbook, but there are 8 computers in my 2-bedroom house.    (5 laptops + 3 desktops)

I used to have a 15 inch. Macbook Pro but I sold it and downgraded to fund head-fi.  My present Macbook can't even stream Netflix full-screen but the audio is awesome.  =]

toshiba satellite l655d laptop and an acer aspire one d150 netbook.

so to answer your question that would be 2.