Summon Monster

How often does monster summoning by the PCs come into play in a typical game of D&D?  I'd have to say before we started playing third edition, it basically never happened.  I'm not sure if it was the casting time of the spells, or the added complexity or what but I don't think I can recall a single time before 2000 where at any of the tables I played at there was monster summoning that influenced combat.  Sure, the DM might gate extra demons in using a demon's power to bring in more of its kind, but the PCs wouldn't be calling creatures from beyond to fight for them.  3E changed that for us.  All of the sudden the clerics, sorcerers and wizards of the party were regularly bringing in celestial bisons and whatnot.  It made for some pretty entertaining combat situations as these short lived and expendable minions came in and were used to mix it up.  To some extent, the concept of summoning creatures from beyond the world always seemed in fantasy like it should involve elaborate expensive rituals and time consuming casting.  The 3E spells were more like hey Rocky, watch me pull a rabbit out of a hat.  I think both ideas work in a game situation, though I'm not sure in a single campaign if I'd want to blend the two styles.  Thoughts?