Hmmmm... Actually, I have more than 4 computers. I only have 5 (I actually miscounted before) that have MC installed.
I have (currently):
1. my Main machine at home (Windows XP)
2. my HTPC at home (Windows XP)
3. my "windows" work machine at the office (Windows XP)
4. our "shared" work machine (Windows XP) -- this is used by everyone in the office for certain tasks where you need a windows box (we're mostly a mac shop)
5. my work laptop (Windows XP) - we loan this out to others for PowerPoint presentations and stuff but I can use it too and I do for MC regularly.
Then, I also have:
6. my main Work machine (MacOSX 10.4)
7. my development webserver at work (MacOSX 10.3)
8. 2 Mac laptops (one Powerbook G4 and one MacBook Pro) -- shared like the above mentioned PC laptop
9. my linux box (Kubuntu) at home (currently in pieces from a move but hopefully soon will be back in action)
10. my IPCop firewall box at home
11. my video recording workstation in our Auditorium at work (MacOSX 10.4)
12. my live streaming box in our Auditorium at work (MacOSX 10.4)
13. my Mac at home (MacOSX 10.4)
We actually also have 1 more windows laptop (Windows 2000) and 1 more OSX laptop (an old G3 iBook) but I hardly ever touch them other than to fix problems.
I also recently decided to replace the "office" main PC at home with a different machine (I'll build a new one out of some parts I have). That box is way more powerful than it needs to be for what my wife uses it for daily (Internet, Word, money management, school stuff, etc). So, I'm going to replace the "office" machine with a new (but less powerful box) and move my "main" PC downstairs into my workshop. That's where I do the majority of my computer work and gaming anyway (well, I do a lot of gaming on the HTPC too). Too often I can't get to it because my wife needs to do schoolwork though!
Plus, our electric bill is getting a bit high, and that machine is sitting idle (or running Firefox and MS Word) with an ATI X1900XT sucking down power like it's going out of style! Moving that machine downstairs (where I'll not boot it up unless I'm going to use it) should save us some electricity too!