Like Engelfire mentioned, with the current rate at which feats are gained, everyone could spare two to get Greater Focus in summoning related spells. I think the durations for combat summons are fine as it is. You can already extend powerful summons like the Skeleton Chieftain or the Direwolf and they'll last throughout a battle.
However, using summons as part of RP is pretty useless atm. It has been suggested before in a different thread, but I would like to repeat it here again. Will it be possible to make an RP version of the different summons that are equivalent to a 1HD creature, without any abilities, but with an extended duration of 1 hour/level? That way, the necromancer can have fun with his minions and the conjurer and blackguard can have fun with their demons. They'll be decorative summons, usable only for RP and to enhance moods.