Seeing friends
 

I'm due to be passing through YVR in the coming months and both times have a layover of 3 to 4 hours. These will be LHR -> YVR -> SEA and the reverse.

We have friends in Vancouver and the surrounding areas whom it might be nice to have a coffee or a beer with, but I was wondering about the logisitics. Will we be able to "get out" of the gate area to meet them at all or once we're through are we locked in as it were? I don't really want to compromise the trip at all by some contrived workaround of reclaiming bags, and rechecking them as I've flown enough to prefer an easy life over complicating things :)

You'll have to clear Canadian entry procedures to go landside. At least enroute to the U.S., you will have to get your bags (dumped in a special area) as you will preclear U.S. entry procedures at YVR. Not sure if you can meet your friends after going to the transfer desk before Canadian immigration (never had to use it since I live here) and getting your bags to go through U.S. immigration & customs.

On the way home, you won't have to do anything with your bags. You could go landside once you clear Canadian immigration - whether it is advisable depends on what time flight arrival from SEA is.