I heard of journald only a couple of hours ago (Tuesday?) and since then some intense discussion is going on. I had a chance to look at the journald material in more depth. I also had a quick look at journald's source, but (as I know) Lennart and I are on the strictly opposite sides in regard to the amount of comment lines in source files (I put half the spec in, Lennart nothing at all ;-)). So I did not try too hard to make sense of the code and my impression is still primarily based on the initial paper (though I have to admit his code is probably simpler as he does not need to carry any legacy nor consider platforms other than recent Linux).
The contra-syslog arguments can be classified in two classes: vaporware and correct fact. In the vaporware camp are things like the hash chaining "security urban legend", the timezone argument (though he is right in regard to current practice inside distros), syslog network transport and compression (this list is not conclusive). Technically correct is the current store format, different log sources, and free-formedness of messages (I prefer the term "semi-structuredness"). This list is also not conclusive.
I think Lennart makes some good points, but discredits the paper somewhat by going overboard at times. It looks like he really needed some hard selling points (I also got this impression by his usage of the kernel.org breakage to promote this effort...). I think his paper would have been more useful if he had argued only those problems that actually exist. I am in full agreement that there are some spots that really deserve to be changed and addressed. Unfortunately, the paper is phrased in such terms that people not at least at the medium expert level on logging tend to believe everything that is stated.
The question is how the actual problems can best be fixed. Is it necessary to create a totally new infrastructure and throw away everything that exists? Maybe. I still prefer the alternative approach: why not extend existing technology? I modeled rsyslog specifically for this reason to be a highly modular system where extensions can easily be added. As far as I understand, syslog-ng has also moved to such a design in the recent v3 version. In rsyslog, I have accepted even experimental technology inside the source tree quickly. Getting a new log store was on my agenda for quite some month (the syslog-ng commercial fork already has it). I unfortunately had not enough time to implement it - and nobody else helped out with it. Wouldn't it have been a good idea to contribute something to rsyslog instead of crafting something totally new?
Another thing that I strongly doubt is if the Linux journal idea will actually manage to solve the logging format dilemma. Microsoft's event log is in place for 15+ years, and app developer still don't use it correctly (as I initially wrote, the Linux Journal looks quite similar to the Windows Event Log). While I think the UUID idea is actually not a bad one, I seriously doubt all developers will understand and use it (correctly). This is a problem with the Windows Event log as well. One needs to know that a lot of high-profile folks are working for several years (10+) on solving this dilemma. Lennart may be a genius, but I have concerns that he over-promises (but I really wish he has success, that would be a very, very big advantage for the community).
One thing, I have to admit, that disappoints me is that Lennart never approached me with his proposal. He knows me (even personally) and we have worked together on systemd/rsyslog integration. I heard about journald first on a Google Alert and quickly after from some folks who asked me what went on. Then I found out that the systemd development mailing list also never mentioned any work on journald. So, to me, it looks the idea was well hidden for a surprise at Kernel Summit. Well done, but not my style ;-) This missing openness concerns me. My decisions in regard to rsyslog were controversial at times and dictatorial at others (and for sure sometimes wrong). And we currently have some big and controversial discussion on rsyslog going on (partly fueled by the arrival of journald). But I have always played very open, communicated what I had on my mind (in advance), discussed and did never try to hide something. This, to be honest, is how I expect work to be carried out on an important system component. I also never met Lennart at any of the standard bodies work on logging. Not everyone runs Linux and probably not even everyone on Linux will run journald. So standards matter.