Do I need a rental car for a 5 days in Vegas?

[fluff]

If I'm there for 2-3 days, I'd get a car, because the cab fare back and forth is almost the same as a compact rental.

For 5 days it's going to start to be more expensive. If you're planning on staying on the strip most of the time you have very convenient travel options anyway (monorail, trolley etc). If you do plan an out of town trip, get a rental for just that day.

Also, expedia.com has had consistently lower prices for the exact same flight/hotel combo than travelocity.com in the past for me.