Ah, I somehow managed to conclude these lock ups were happening more frequently. But now I understand they are infrequent and, as such, I've lost interest.
Well, almost.
The longer it goes between shut downs the more main memory gets consumed; each time you visit a web link, each browser tab you have open, each application you have running (and there are a lot of apps running that you don't even see) all consume main memory. Some apps when closed don't release the memory as well as others.
Joe's practice of daily shuts downs is a bit heavy IMO, but faultlessly effective in cleaning out the cob webs that build up. My work laptop can usually go a week or two just being put to sleep before I notice things are behaving wonky, a shut down clears it up. My home pc will go for weeks, sometimes months, being put to sleep and woken up but it doesn't get a lot of use.