The iPhone OS 3.0 software adds the ability to save short voice memos on your iPhone. In addition to saving them, you can rename them and trim them down (like you can with videos taken with the 3GS).
To rename a voice memo, go to the app's list view and tap on the right arrow symbol next to the memo you want to rename. This takes you to the info screen for that memo. Tap on the right arrow in this screen and you are presented with a list of labels you can attach to the memo. The "Custom" option at the bottom of this list lets you create a more specific name for the memo.
To edit the memo, tap on the "Trim Memo" button on the Info screen and you are taken to screen with a yellow trim bar. Slide the left and right edges of the bar to change the beginning and ending points of the memo. To preview your changes, tap the small arrow icon to the left of the trim bar. When you're sure you like the edits, hit the large yellow button labeled "Trim Voice Memo." Note that you cannot go back to the original memo after you hit this button.