I have a pretty horrible short term memory, so whenever I think of something that I need to remember for later I like to jot it down on a scrap of paper. I was addicted to pocketmod for a long time, but now that I no longer have reliable access to a printer, I had to come up with a new notepad.
I tried moleskine and 8.5x11 sheets folded in quarters, but both of these require you to carry a pen with you. Since I'm already always carrying my phone, keys, and wallet, I don't particularly like adding a notebook and pen to my already full pockets.
If my phone, a Samsung Blackjack, played a little nicer with my Macbook, I would use it more for writing notes and such. But even with Missing Sync, it's a pain in the ass to make my phone do anything with my laptop.
Here's the solution I finally came up with to easily use my phone to jot notes for myself: Post notes to gmail via text message
I wanted to make this as easy as possible, so I created an address book entry on my phone just for this purpose. I named it NNnotes, so I can just tap N 3 times to bring it up. The only contact info associated with this entry is my gmail plus a flag I use for filtering the notes once they arrive in gmail:
You can append anything you want after the plus sign, but I kept it simple and used notes. I think I originally heard about this technique on Diggnation or TechTv, but googling for more info lead me to this lifehacker post where you can read a bit more about making disposable gmail aliases.
Also, you don't need a gmail account for this to work. You can make a shortcut in your address book for any email address and send text / mms messages to it.