Depends entirely on where you fly, and what time of the day you do it!
My experience is mainly in Asia which is mostly quite good. HongKong-Singapore is a route that you will often be held down on. For example you flight plan FL370, but are held down at FL290 for the whole flight. A lot of this is due not to other aircraft on your route, but aircraft on routes which cross yours.
A big part of the cruise can sometimes be monitoring other traffic and knowing who is blocking your level. Once they get a climb or turn off the route you jump on the radio and request their level before someone else does!
It may sometimes even be benificial to slow down for a while to get the required separation to climb up behind another aircraft. Might cost you a few minutes but it could save you a lot of fuel.