I can also confirm that this issue has been fixed. Finally, I can play Minecraft again! Thanks!
It's rather sad to say, but there is absolutely nothing Mojang can do to fix those issues as they reside outside of Minecraft and thus influence of Mojang. (Source)
Is that really true though? Mojang profits from the open source LWJGL library. I can't imagine it would break Mojang financially to either assign a developer to work with LWJGL upstream or to issue a bounty for a fix. If not for Mojang's paying customers, then at least in the spirit of open source software.
The Mojang home page says, "Minecraft PC edition is about to hit 10,000,000 sales." So, after massive commercial success using an open source library, you're going to belittle paying customers who use an OS with "overstated" popularity for being frustrated that their purchase isn't working as expected?
Webroot may be causing related issues for some users, but that doesn't appear to be the primary cause of the problem noted here. I also did not buy my Mac at Best Buy, nor have I had it serviced there. The fix, according to Kumasasa, is to use the new launcher.
As Kumasasa noted above, you can download the launcher here: http://mojang.com/2013/05/minecraft-snapshot-13w19a/
I personally have not seen the problem recur since using the new launcher, either running the latest snapshot, or with the 1.5.2 release. Though, since the issue was intermittent – for me, it might happen every minute or two, or every twenty minutes – so it's difficult to confirm for sure without a lot of playing time. It seemed to happen only when holding down a key for an extended period of time, and I've spent a good ten minutes mashing keys as long as possible to try to recreate the issue and haven't been able to do so.