ATC may well have forgotten to hand you over, but isn't there a point at which you should be thinking to yourself, "I need to be changing frequency around here?"
Absolutely! Since the advent of FMC and EFIS and relying on these items rather than looking at charts the level of situational awareness has decreased. In the days when we didn't have such devices we were very aware of FIR boundaries and sector change over points. Whilst I would agree there is more sectorisation these days it surely wouldn't be beyond the wit of the software guys to portray FIR boundaries on the EFIS ND.
A few years ago I a got the high level chart covering the Bay of Biscay area out and my FO wasn't even aware that enroute Comms frequencies were on the chart - sometimes useful if you lose comms with ATC.
Has any in depth research been conducted to find out why and where loss of comms takes place? Are there certain geographical points where this is more likely to happen (rather like hotspots shown on charts for runway incursions). Are some radio fits more disposed to loss of comms by inadvertently turning the volume down? Do pilots know how to verify correct receiver operation (e.g. by momentarily lifting the squelch control).