I'll disagree with MapleLeaf. After all, it depends a lot on where you are flying from. If you're coming from Boston, the flight to Vegas may be almost as long as the flight to Europe. But a flight from L.A. to LAS is a poor use of miles in either class.

ML is correct that overseas premium travel does offer the best "value" for your miles, that is, savings over what the ticket would have cost in cash. But where do you plan to go? If you don't plan to travel internationally in the next couple of years, then don't hesitate to use miles domestically. Just make sure you price out a cash ticket first to make sure there's not a super-cheap alternative.