That last thread didn't seem to turn out well, so even though I'm a new member I thought I'd take a stab at getting a discussion back on track.
From a general play standpoint, disc seems to be in a fun, if not powerful spot--the standard "fun" spec grabbing AA/Atonement and the direct heal buffing talents works well for five mans and farm content, if being a bit underpowered compared to other healers. Anecdotally speaking our disc priest, when acting as a tank healer, couldn't compete (but this is possibly because she had been geared for bubble-spamming prepatch). Part of the problem is not having access to Inspiration, which just makes disc a not-very-good choice compared to other options.
However, for the majority of guilds, disc will still make H-LK significantly easier, though most people may find that two disc priests are required. Due to the Borrowed Time nerf as well as other haste losses, the haste rating GCD cap for disc (assuming 2/3 Darkness) is something around 740, which is pretty high considering all the mastery required to keep shield propped up where they need to be to handle infests on Heroic 25. A perfectly geared (full 277 haste/crit gear, with crit reforged to mastery) disc priest -should- be able to 1-bubble the infests, but my own guild (and several other late-comer LoD guilds) are finding themselves forced to move to a 2-disc strategy because our priests can't get their GCDs low enough.
Overall I think Disc is a very fun spec, if not as powerful as it could be, with a lot of potential for growth at 85. As far as I can tell Blizzard doesn't seem to think there's a problem with it so it's not likely to be buffed before Cataclysm. Love it or hate it, it's here to stay.