ALJUK  Why not just change the system settings? (that's what they're there for). It won't cost you anything either...  
(Version 2.5.2)

DAOHEAD  Consider Caffiene (http://www.macupdate.com/info.php/id/24120). Does it nice and simple and for free.  
(Version 2.3)

GAZMAN  Doze (http://www.macupdate.com/info.php/id/20699) does exactly the same thing, is free, and works flawlessly on my Intel MacBook.  
(Version 2.2.2b1)

MAC0852  Simply doesn't work on my Macbook running 10.4.8. I close the lid, it goes to sleep.  
(Version 2.2.1)

SCIENCEGUY_AE  DO NOT USE v.2.2.1 ON MACBOOK!!

I just spent an hour on the phone with AppleCare support, only to find out that Sleepless 2.2.1 had badly corrupted the PRAM on my Intel Core Duo MacBook. Since Sleepless claims Intel compatibility, it may be an incompatibility with Apple's recent SMC firmware update.

Only one use of this software had completely crippled my system, preventing even the most basic of firmware functionality, including the boot process. This is a bad bug. DO NOT ATTEMPT!!  
(Version 2.2.1)

NIRSUS  The last version of this worked wonderfully for me. But for some reason the system tries to automatically log out while sleepless is running which interrupts whatever program I want to leave running over night. This is on an iBook G4 1.33ghz with OSX 10.4.5, and leaving the lid open with the display backlight off.  
(Version 2.2.1)

MATT DELL  I L-O-V-E this program!!!

Much thanks to the author for providing this resource to me. I share a 20" monitor between my Powerbook and my PC through a KVM, so whenever I would switch to the PC, the Powerbook would go to sleep .

But now thanks to SleepLess, I can keep all my active connections open on my Mac while I use my PC.

Thanks again to the developer!! 5 stars all the way around!!  
(Version 1.7.1)

FLIPTAK  I found elsewhere that your ibook/powerbook must be plugged in for sleepless to work for longer than 3-4 minutes before crashing the system. It would be good to add this to the documentation. Obviously this limits the appeal of this program to many who wanted to be able to plug into their laptops sitting in their briefcases. I will still find it useful, as I can plug into a car adapter.

Another problem, which I haven't found a solution for, is that Sleepless simply won't launch on my Powerbook. This seems unrelated to the version of OS X, as it does work on my iBook and both are running 10.3.9 The Powerbook is the original 15" TiBook, 400 mhz.   
(Version 1.7.1)

ANONYMOUS  Please don't use this program if you are a laptop owner hoping to run your computer with the lid closed.

I've tried this program on 3 different editions of powerbook and all do exactly the same thing:

Run Sleepless

Close Lid

Computer stays awake. Great.

2 - 5 mins later computer shuts down. Dead. No chance to save.  
(Version 1.7.1)

ANONYMOUS  I have a PowerBook G4. After I read "Read me"

"Attention!

Using your portable Mac with closed lid can lead to serious system heat problems!"

What do you mean? Can I use it without a trouble?  
(Version 1.7)