This week Brad (who is like 10 hours in now I guess) mentioned how they roll out battle mechanics slowly (which seemed odd to me because after the first 2 hours basically everything is there except for what you would label as endgame) specifically mentioning how he just got his first summon. Now while technically that is part of the battle mechanics and the first one is shown to you pretty late his comment made me realize I have only used a summon once in the game so far. The combat itself has been fun and engaging enough I never felt like using one, for the time I did most of the animations vs damage done increased battle time significantly enough for me not to use Odin again. 
 
In a nutshell I guess unlike Brad the entire time I've been playing the game I always thought of summons as more of a story mechanic than a battle mechanic given to you 6 or so hours into the game. What about yourselves?

well they are pretty useful. Personally though i try to only use them as a last resort. The ace in the hole. 

I find them very useful as a 'oh crap' button.  Remember, when the summon leaves your entire party is fully healed/revived/cured of all status effects.  If I've spent a while in a fight (some chapter 11 fights have goal times of 5-6 minutes) and don't want to start all over, it can be a massive life-saver. 
 
Also, it's the best way to get the Limit Break trophy prior to getting genji gloves.   
 
I'm partial to Fang's, Vanille's, and Sazh's eidolons generally.  Not too big on Light or Hope's, Snow is alright.  

They're useful for the megalixir effect, but in terms of damage potential you're better off sticking to the 3-man team.
 
I prefer Sazh's summon because it knows it's ridiculous. I don't think Snow or Vanille have any idea how goofy they look, but Sazh is in on the joke and rolls with it.

The fact the only your main can use the summon pretty much keeps me from experimenting with them. 
 
I do use Odin when i get into an ambush like situation just to thin the herd

I never used them properly though the whole game. It was only when they force you during the story. I've never felt like I needed to use them so I didn't, especially since it eats into my precious tp that I pretty much used exclusively for scanning.
 
That said though I did use Vanille's one a couple of times today to exploit and ultimately kill a few adamantoise.

I haven't used them much either. I think I've only used them is three or four times total thus far. They're a good last resort, but I can often get myself out of any bad situations without the help of the eidolons, so they're usefulness isn't very high.

They're excellent for dealing damage outside of the ATB, and they help a lot with boosting the stagger meter on bosses.

" They're excellent for dealing damage outside of the ATB, and they help a lot with boosting the stagger meter on bosses. "

28 hours into the game I ended up on Gran Pulse. There you'll have to experiment with which enemies you choose to fight because you'll get slaughtered.

" 28 hours into the game I ended up on Gran Pulse. There you'll have to experiment with which enemies you choose to fight because you'll get slaughtered. "

" @Kombat: I just got to chapter 10 (right after that nasty battle on the air ship), how much longer until I get to Gran Pulse? For what it is worth, it took me about 23 hours to get to this point. "

I have only used Odin so far, because I just love haveng Lightning in my party. I'm going to wait until I unlock more roles for characters to switch up my current party of Hope, Lightning and Snow so I can use some other Eidolons. Hope's Eidolon has 37,000 SP... compared to Snow's mere 13,000, that is ridiculous. 
 
I didn't use them much at the beginning, but now that I'm on  
 

" @Kombat said:

" They're excellent for dealing damage outside of the ATB, and they help a lot with boosting the stagger meter on bosses. "

Which auto resets when they leave. "