I'm in the process of putting together a journal-based online RPG, and am contemplating a few different ways to handle the dice rolling:
1. I roll all the dice. This keeps control in my hands, but slows down story threads until I can actually make the roll and post the results.
2. I let the players make their own rolls. This speeds up story threads, but takes a measure of control out of my hands. I also have no real way to know if players are being totally honest about their results.
I am currently contemplating a modified version of #2, where I have the players use an online dice roller (I'm familiar with Irony.com, so I'd probably use that) and post the results in the thread. Granted, I'd still have no real way of knowing who was cheating, but that's the price I'd pay, I suppose.