Thanks for all the well formed answers!

It seems that SMN basically comes down to having DoTs up at all times, proper use of pet CDs, knowing when to Bane and when to Fester, and simply spamming Ruin (Ruin II whenever you have off-GCD spells to cast) as filler. Somewhat in that order. Any other tips for an aspiring Summoner?

I also have a more specific gameplay question:
When mobs or mob-like things spawn that needs to be burst down quickly (for example Napalms in CT, Conflagrations/Dreadknights in Turn 5) what is your course of action? Whenever Bane is available for spreading it should of course be used, but when it's not? Is it best to put up your three DoTs and then Fester, or just Bio and Ruin-spam?