I intercepted this e-mail of thoughts from a friend that had some thoughts on the summoner. I've not searched through all these threads to try to pick out the answers - I admit, I'm lazily posting this to see what thoughts are out there on these. Really I'm just trying to get some perspective on what the rules say as well as on what other GMs think is reasonable. Thanks for any thoughts...
•Using your Summon Monster SLA is a standard action that immediately ends any previous use of the SLA. You can use this to squeeze out two full attacks in a single round. Have a previously-summoned monster attack, then take your turn, summon another monster (dismissing the old one) and have that attack too.
•While summoning another monster with your SLA dismisses an old one, that doesn't apply to summoning another monster with your spells. If you keep one or two Summon Monsters in your spell list, you can have multiple summons out at once.
•You can have your Summon Monster SLA and your Eidolon out at the same time. Just use the Summon ability, then take 1 minute to call your Eidolon. (The rules say you can't use your Summon ability while your Eidolon is active, but there's nothing stopping you summoning your Eidolon while a Summon is active.) Since your Summon lasts 1 minute/level, this is a great way to double your hitting power if you have some prep time.
•You can even get a summon and your Eidolon out within two rounds! First use your Summon ability, then cast the Summon Eidolon spell. As a nifty bonus, this lets your Eidolon gain +4 to Strength and Constitution if you have the Augment Summoning feat.