I generally clock most games I have.. clocking the game doesn't mean doing everything possible, rather finishing the game up to the point I defeat the final boss.
if I really like the game I'll either clock it multiple times or play the game's end game (if it has one). Games that I've done that with include (but not limited too) Diablo 2, Doom, Sonic 1, Disgaea 3, quake.. etc
Its very rare that I don't clock a game, however I might take some time to clock games that I either find boring or extremely difficult. MGS4 I lost interest in during Act 3, but a few months later I got past the 'follow the guy' mission and ended up flying through the rest of the game, enjoyed it. NGS I had possibly a 2 month timespan between making it up to the final level and finishing it, due to getting too frustrated at dying which effected my decision making. Demon's Souls that might happen too as well.
I do have some games I haven't clocked, if it isn't on my current "playing" list its on my "going to play" list. Games like Cross edge I own but haven't even unwrapped so I don't consider it a failure to clock yet :p
