Could you mention the Glyph of Holy Fire (increased reache for atonement), please?
From Darkness Comes Light works well together with Atonement if you want to keep an eye and Grace on the tank.
Interaction of Twist of Fate and Atonement is very strong and makes it more interesting as well; it double dips and you get an incentive to pick targets for your dps spells. On most fights where it is a good talent for Shadow it is good for Disc as well.
Could you mention Borrowed Time in your description of Power Word: Shield (you do later on but I think since it only affects this spell and always this spell it could as well be part of the spell as disc and you put rapture up there so why not mention both and put rapture where it belongs), maybe even hint that it is a good idea to cast penance or instants (especially Holy Fire/Solace) after it if you want to use those spells anyways.
The strength of atonement is that while it has a cast time the target of the smartheal is choosen when the cast is complete.
---------- Post added 2013-03-16 at 01:29 PM ----------
This is incorrect. Nochannel macros do delay your next cast until the cast is finished on the client, while the ticks are generated on the server, thus your nonchannel macro will start the spell cast after (cast time of pennance) + 2*(latency), but with a castbar that shows latency you could have started the cast after (cast time of pennance) + (reaction time).
Since you have a visual help and can guess when the cast time is up in advance that reaction time can be quite short and will be shorter than twice the latencey for those areas where latency is an issue.
It is twice the latency (plus server reaction time) since the castbar of the client starts only after the server got the information that you started to cast pennance and replied to the server that the spell is registered as being casted.