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I'm in college and I use a MacBook as my main computer. I basically just use it to do Word processing, surf the Internet, and email so it suits me fine.
 
I'm 15 and my MacBook has been my main computer since November 2007. It's still running as good as it did when I took it out of the box. I use my MacBook for around, on average, 3-4 hours a day...rarely lags, and it's always ready for action. :D
 
While this thread is already long enough, I'll add my quick 2¢.

My 2 main computers are listed in my sig below, but in terms of hours per week, my MacBook gets far more use than the Mac Pro. So, in a sense, my MacBook is my main computer and my Mac Pro is my secondary machine.

I use it out and about often, attached to a second (21") display at work, and frequently attached to an Apple 20" Cinema at home.
 
Im curious how many hours per day do you guys use your books for?

These days with my current work at least 5 hours a day and it is never switched off. It is plugged into an external 20' wide screen monitor which auto-powers down if I am away.
 
You can most definitely use a Macbook as your one and only computer. I have done so for three years now and it is great. Before then I had a windows laptop that I used and my only computer. Laptops are able to handle anything and everything that a desktop can.

I even played WoW for 10 hours a day for a whole year and my guy never failed on me. Aside from that, they can even handle pro applications like Adobe Suite amongst other programs.
 
I hate to admit, the MacBook sees me more than my iMac does, definitely can use it as a main computer.

I do still call the iMac my "main computer"
 
3-4 hrs per day, sometimes longer, and most of it on its 13" screen. At work I'll often plug in a 21" display and use both when preparing Keynote presentations.

I use mine for anywhere from 10-14 hours per day or more.

I'm usually online in the morning before I hop in the shower, checking on my email.

Travels with me to my client and is in use all day, often in dual-screen mode to an external HP L1906 (it sucks, but it's what the client provided). As an aside, I am almost always running a WinXP VM (in Fusion) during this time.

In the evening I am online for another hour or three doing various other client work, running my business, or playing a game.
 
These days with my current work at least 5 hours a day and it is never switched off. It is plugged into an external 20' wide screen monitor which auto-powers down if I am away.

6+ hours a day. Usually Adium, Firefox, Photoshop, iTunes, uTorrent, Teeworlds, Word, often all at once. Also Pro Tools runs particularly well on this machine. Perfect as a main computer if you don't need to use 3D intensive programs.
 
I have used a MacBook (Rev A black and now 2.4 alu) as my primary machine for around 7 months. Before that I used a PowerMac 2GHz. I switched to the MacBook because the PowerMac was too noisy and hot in my room.

I haven't had any problems using the MacBook as my main machine. I plug it into a 20" ACD while I'm at my desk.

We have around 60 MacBook's being used by staff in the Faculty I work and they've all been just dandy.
 
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