I wrote a guide for summoner necro. You're free to check it out to get some hints on how to gear up/ where to put skillpoints and how to finish ubers in lategame:
viewtopic.php?f=40&t=5045It may be a lot of information, but it's definitely worth the read.
btw: didn't you put points into bend the shadows? Because with that skill you can teleport. Your totems will teleport with you and you don't have to recast them all the time. I'm just mentioning that because you didn't say you put a point into it.
And Embalming improves the life of your summons and yourself. It's actually a nice skill to put points into because you and your summons get tankier and your manaregen is increased by a ridiculous amount.
And what "not for keeps" said it correct except point 2: You get 1 maximum skill level on each skill every 6 levels. This was implemented to balance the skills, so you don't put every point into 1 skill and crush everything with it. You're basically made to spread your skillpoints and enjoy a variety of skills in order to not get bored that fast.