Got back into DD with the new patch and I've been playing a mage type character. I've finished most of the initial village quests and am now fighting Orcs in the surrounding wilderness so I'm still pretty early on in the game.
In this type of game I tend to favour summoner types so I've got Summon Rat lvl1 and Summon Skeleton lvl2 but so far they seem to be utterly hopless abilities. My rats attack something nearby but are killed or wander off before they do much, My Skeleton is even worse as it just tends to wander off in a random direction and I've yet to see it attack anything at all.
I might be summoning them to soon as I tend to summon when not already engaged in combat as by the time I'm in contact with the enemy I tend to rely on Meteor Strike as my main combat spell.
Am I missing something or have I just wasted the Skill points on the Summoning skills ?

The third post on this thread seems to address your question.

I've tried playing with them as well they don't appear to follow you from room to room properly. Not sure if they improve later but so far compared to diablo 2 summons they seem to suck.
Edit: cheers Stuff, It appears I need aura of command to at least get them to hang around my guy, will test it out later.

Stuff - thanks for pointing me in the right direction, I'll have a go at developing Aura of Command/Master Summoner/Transfer Powers and see what the result is.
Ralackk - Diablo 2 was my comparison as well, my summoner there had a small army of skeletons and an elemental/golem and it was the rare battle when my character actually had to attack anything directly. I think I might just need to get used to the different power level of the summon ability in DD, it also might be more fun not being able to rely on my army of undead to deal with everything for me.

I gave up on summoning so it would be great to hear what is necessary to use it properly . . .=)

The point is the skeletons dont have to die for you to summon new ones. So if you need to reposition the skeletons just summon them in the new postion, the old ones will then die. The mana cost is trivial.

I found the skeletons great for holding up mobs whilst I blinked in with arrows and freeze.

I like summoning on any game I play, but normally I do it in combat

Summoning is OK, but it's nowhere near as strong as in D2. It works fine, though, they just follow you around and get in the way so you don't get swarmed. They don't do oodles of damage so you'll likely end up doing lots of the actual killing yourself (especially at higher levels), but they're very very useful as a distraction. Don't bother with the vermin, they're useless. The skeletons are useful but not very strong. You'll need to rank up a few times to get a decent crew going. Demonic Aide is my favorite, and I often put at least 3 ranks in it regardless of what type of character I'm playing. Master Summoner is a must if you plan on doing any of the summons, but I haven't been impressed with Transfer powers. I'm not sure what "powers" exactly are transferred, if any... do they benefit from your skills, or do they just get a Strength and Agility bonus? I'm not sure anyone knows.

Also beware the "Shadow Warrior" skill in the Warrior line, it's not actually a summon, though its description makes it sound like one. It's just a pretty lame range-damage spell.

Some tips on summoning from the official forums:

http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Main=3668&Number=96393#Post96393