Recently, there have been a lot of discussions around how WP stores authentication cookies.
It is nice that the developers are addressing this design flaw.
The change was made on Dec 17 (revision 6387).

However, this change made my blog management pages fail to show up, rendering my blog completely unusable.
I don't know what happened, but I temporarily worked around this issue by rolling back the revision to an earlier date.
The command for that is:
svn up -r {2007-12-16}

PS: A little bit about how I ran into this problem and found the cause.
Although I was aware of the cookie bug of WP, I didn't know the developers had already started to fix it.
I simply do a svn up every few days when I feel like it.
So, today I did a routine update and found my blog unusable.
Then, I tried every date before today and nailed down the problem in the 12-17 version.
The next thing I did was to examine the change logs and the diffs:
svn diff -r {2007-12-16}:{2007-12-17}
svn log -r {2007-12-16}:{2007-12-17}
Judging from the change logs, my immediate gut feeling was that there must be something wrong with the "new secure cookie protocol".