By default, recent Macs ship with their hibernate mode set such that when your Mac goes to sleep, contents of the RAM remain stored in the powered-on RAM in addition to written to the hard disk. The is called safe sleep mode because in the event that your computer loses power during sleep, the contents of the RAM can be read from the hard disk where they were dumped before sleep. This is why it is possible to change your battery while your MacBook is sleeping with this default sleep mode.
That's all great but with more and more people using 2GB or more of RAM, it takes quite some time for the contents of the RAM to be written to disk and the laptop to begin sleeping. Why is this an issue? For me, I always sleep my MacBook Pro when going from class to class. Waiting a minute or longer (4GB RAM) for the laptop to begin sleeping means I have to wait to put it in my bag or risk damaging the hard drive as it's busy writing, not to mention the potential for heat build up with the laptop tucked away in my bag. I don't really care if the laptop enters safe sleep - I don't change batteries in sleep mode that often anyways and the possibility of the battery just falling out isn't too great.
With mode 0, it takes ~5-10 seconds to sleep compared to ~ 1 minute with 4GB RAM.
In this case, my solution was simply switching the sleep mode to old school mode 0. Everything remains in powered-on RAM and that's it; no hard drive mumbo jumbo to slow me down. MacWorld has an old but still relevant post about how to accomplish switching between sleep modes.
In a nutshell, your Mac is currently in sleep mode 3 and you want to go to sleep mode 0. Just run the following command in the terminal, enter your password when prompted and test out your fast-sleeping Mac.
sudo pmset -a hibernatemode 0
Just don't blame me if your battery does actually fall out while your mode 0'd MacBook is sleeping and you lose your session data. Will you try out this sleep mode for speed or are you more concerned about "what if" cases and like your RAM dumped to disk before entering sleep?
Now, if only there was a terminal command I could run so the optical drive stopped making that stupid sound everytime the computer wakes up.