It all depends on your usage (like everybody said already). My friend has a small 110 compressor llike that (speedaire) and after a few nuts/bolts with theratchet you need to wait for it to pump back up. If you want to make regular use of air tools (or if your lazy like me) and your budget allows, Id look into going bigger. Something in the 10cfm range at least.
When you go to home depot, hey advertise their tools as only needing "5cfm" but thats BS, because its based ona 25% duty cycle.... It uses 5cfm over the course of a minute when te tool was actually run for 15 seconds out of the 60. To get an idea of what the tool needs to run non stop all day long, multiply it by 4. Multiply it By 2 or 3 and you should be happy with how the tool performs.
Jim