Our 3 yo Dual USB MacBook (Intel dual core) is having intermittent wake from sleep problems. It's on a WiFi network and running Leopard - 10.5. On lifting the lid it spins up then hangs with a faint blue screen. There's no cursor.
I haven't found a fix yet, but here's a list of what I've tried . They're listed in the order I'd suggest. Of course the first thing to do with any ill-behaved machine is to check that your backups are good...
- Run Safe Mode start, (aka Safe Boot) then restart 
- Remove share mounts
- Login items - remove all
- Clean out list of remembered WiFi networks - Network:AirPort:Advanced. 
- Do not inactivate the ethernet port - even if you don't use it. Delete all Locales. 
- Disable Bluetooth
- Update Flash (or consider removing it forever)
- Input Managers - remove all. They are Satan's tool.
- StartupItems - remove all from Library\StartupItems and ~\Library\StartupItems if it exists. Do not mess with System\Library.
- Onyx: check corrupted preferences, check disk, delete caches including font caches
- Onyx: Repair Permissions :-) 
- Install disk, run disk utility check disk
- Reset SMC 
- Zap PRAM 
- Run hardware test in loop mode on install DVD
- Remove or update any low level software
- Look in /System/Library/Extensions for ideas, but dont' mess with /System. Look in Library/Extensions.
- Cisco VPN for example - uninstall requires terminal
- Retrospect Client 
- Fusion is another - it loads early. Update it.
- Console.app: Look for messages on startup. Unfortunately Console captures a vast number of warnings and error messages even in a "healthy" system.
- Disable Safe Sleep (more a Leopard than Snow Leopard option?)
- Look for more ideas here: Tutorial: Dealing with Wake-from-sleep issues | MacFixIt - 2006
- Reinstall OS X (desperation move). If you're on Leopard, might as well upgrade to Snow Leopard.
- Send out for repairs - likely a hardware issue. Bad memory can do this and problems may not show up in the hardware test.
I'll update this post with the eventual outcome. As of this moment I'm trying Permissions  and SMC reset (more likely to help) and I'll try run the hardware test tonight in loop mode.
Update 12/18/10: The hardware test worked. The problem is much better. I wouldn't say it is perfect, but clearly some of the above measures helped. The two I'd most favor are "clean out list of remembered WiFi networks" and "reset SMC". I suspect this problem is less common with 10.6 and that, at least with 10.5, there are many contributing factors to "wake from sleep" failure. The fixes I made reduced the frequency, but it will still occur.
By way of comparison, there were NEVER any issues with the pre-hibernate sleep mode of 10.3 and MacOS Classic, but XP sleep mode is completely unusable. (I've no experience with Win 7 sleep.)
Update 6/17/11: This problem resolved. I think it was finally fixed in 10.6
- Gordon's Tech: Things to do if your Mac doesn't boot (2/2005)
- Gordon's Tech: My 10.6 iMac is crashing - a debugging exercise (2/2010)
- Inquirer confirms apple macbook pros have nvidia bad bump material (12/9/2008)
- Can’t Wake MacBook Pro from Sleep (5/2008)
- How to Turn Off Safe Sleep
- Set newer portable Macs' sleep mode (return to the good old days - 10/2006)
- Tutorial: Dealing with Wake-from-sleep issues | MacFixIt - CNET Reviews (3/2005 - problems were more common then)
- Solving Macbook Wake from Sleep issue | Tancredi
- Computer sleep vs hibernate | Scott Gruby’s Blog 12/13/10
 OS X has reams of permission related issues. I have never, however, seen repair permissions help with any of them, much less anything else. It always finds things to "repair", but the "repairs" fix nothing. Repair Permissions is the OS X equivalent of a disconnected thermostat. It's there to distract the customer. Still, when all else fails, I suppose it's worth trying. Onyx will conveniently run Repair Permissions.
 Safe Boot, loop mode hardware test and zap PRAM all need a wired keyboard. There are terminal workarounds for Safe Boot.
 An Apple identified cause of wake from sleep issues - Intel-based Macs: Resetting the System Management Controller (SMC): "A portable Mac doesn't appear to respond properly when you close or open the lid." I have noted that sometimes the green light on my magsafe connector doesn't come on ...
 An infamous Discussion thread on MacBook Pro problems is a good source of ideas.
 I had at least 20-30 in my machine. I removed every one.
 I have done this in the past, but not on this machine.
 I had a leftover version from when I used a Win XP Retrospect Pro backup server. I had to find an old installer to safely uninstall this low level app that runs on startup.