I used to play her alot and I still would if i hadnt cut back on my LoL alot recently.
I had very good results on lane since she is a very good anticaster.
You have to make use of that advantage alot though, since as mentioned above, she is not the best damage dealer in a teamfight.
With a little luck you are against one of the squishier casters who will even later go 50% with one of your silence, leaving them useless for a good part of the teamfight.
For Items, I consider Rylai's to be absolute core since it actually gives you killing potential against people who know how to run away from you, and your range on starcall will give you a need for some tankyness as well.
Ionian boots make you alot more useful and i ended up sticking to them most of the time. though i stopped playing around the time athene's was released and i couldnt try it out much, so it might be good to take pen boots and get an athenes very fast. need to try it.
In teamfights: If you get focused, use your silence on the most devestating abilities your enemies bring, keep yourself alive with heals and slow everyone with a starcall and hope to god your team capitalizes on the fact that the enemy just wasted 2-4 ultimates.
If you dont get focused keep starcalling untile every magic dd does truedamage.
EDIT: It must be noted here, that 10 casts of starcall hitting 3 people at around 200 damage each will amount to 6k aoe damage in a teamfight. paired that with a 0.7 ratio on silence actually gives you incredible damage if you manage to draw the fight out long enough.
She is best employed in a tanky team since mitigation makes more use of your heals and them not instantly dying makes your long cooldowns a bit more usable.
For skill order, i dont consider the starcall nerf an issue since i used to max silence ( that makes oyu untouchable against most mids, and youchunk them down decently) i only use starcall to push the lane when i sent someone home ( that is the main way to build an advantage early for soraka and its been tried and proven to work in about 100 games for me)
The heal is usually the last thing i max. And i dont hesitate to use my ultimat for sustain on lane ( also nice to bait with it, but the high likelyness of facing an ignite makes this rather tricky, so better be safe than sorry)
EDIT: I actually played her mid when you could infuse yourself, and then it made sense to get a few points into the heal, but with that gone its just too much of a mana sink, considering how safe you can stay apart from actual kill engages.
Now people will check my profile and see a rather pitiful rating, and that is because i rarely ever played ranked games but stuck to normals with my friends.
I have been matched against some pretty high rated players though and beaten a few of them in lane.
So this is not an utter **** build, but one that depends highly on conditions like enemy team/your team, the likelyness to beat the enemy mid on lane as soraka ( some champions just flat out cannot handle her)
EDIT: She compeletly destroys morgana on lane and can deal well with her in teamfights ( ult counters ult kinda thing, at least if you dont get stunned and decimated instantly) , and that might be her strongest advantage in more competitive play.
And yet another EDIT: after getting the core items mentioned above, i usually built straight ap ( maybe an abyssal cepter for funzies)
Played properly, you will never die on lane and will devastatingly win most lane matchups, but she isnt a pubstomper by a looooong way. You need the right picks and a team that knows how to deal with not having insane focus damage from the midlane.