I've to jump in just to comment a bit about shadow priest DPS in general - during my entire experience of Naxxramas, Obsidian Sanctum (+3D, when it was hard), Eye of Eternity, Ulduar, ToC - shadow priests we had were constantly on top of the damage meter.
Before we get into the whole "oh the rest of your guild sucks then" comment, if played properly - a shadow priest can be an asset in progression raids.
I could go into discussing how a SP contributes at certain boss, but that's pointless.
If you manage to play properly, meaning not dying, positioning yourself so you don't have to move (a lot), executing the rotation as perfect as you can with huge FPS drop and ping increase that you get in the raid, keeping dots at multiple targets, using your AoE when it's the most effective - you will do high damage.
During Ulduar progression, we had a shadow priest being on top at several encounters (1st - 5th place). At Yogg + 1, that same SP had 7500 dps when the boss died and was having between 6500 - 7000 dps at Northrend Beasts Heroic. Consequently, that was by far the best player and the best shadow priest I've played with, but on the other hand I do believe there are better players out there.
Common misconception is to dismiss a shadow priest as a good dps, but due to the nature of encounters a SP can dish out quite a nice chunk of damage. It is true that every other class can do more at encounters like Patchwerk, but those encounters barely exist anymore.
So to conclude - in order to perform optimally, you do need a timer that shows durations of your dots at your target(s) and a timer that tells you when your abilities are off the cooldown (such as Mind Blast). The rest is just casting them in such way that you refresh VT millisecond after its last tick and to cast MB the moment it gets off the cd. Level of complexity of such action is on par with using a spoon to feed yourself, so it's basically a matter of setting up your UI to show you relevant information.