Moisture comes from within the roast as it renders. No need to worry about drying out a butt. For slicing, some folks say remove it at 180-185. For pulling, cook it till the bone wants to fall out when you tug on it. If it's boneless, cook till it's probe tender. Either way, it's important you rest the meat for at least an hour (I prefer 2-4 hours) before serving.
If you want to save time the next go 'round, start the cook at 245-250, then ramp temp up to 300ish for remainder of the cook. You'll cut the cooking time almost in half, and the results will be just as good.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)