I agree logs are far from perfect (as I said, I much prefer email as a medium for discussion). Nevertheless, it sure helps to be able to point to the logs 5 years later and say - that was why we thought it was a good idea. In this respect it is the conversation that is important not the decision.
Why would you want to know the reasons for a decision 5 years from now? In 5 years time we should be concerned about the present and the future, not the past. When we make decisions in 5 years time we should do so based on reasons that are relevant then, not on what took place in an IRC discussion now. It's important to keep track of decisions that are made because they could have lasting effects, but the reasons for them are far less important.
Personally, I would prefer it if all IRC sessions were documented (in the sense of meeting minutes) and reported to the mail list for archiving. However, that is a labour intensive process and therefore unlikely to actually happen. I'm suggesting logs as a nice middle ground that requires minimal effort (and again, I acknowledge the community is now looking at this option - thank you)
Once we have a board, formal meetings will be minuted. Minuting free form discussion isn't just labour intensive, it's impossible. You could possibly put together some kind of summary, but it wouldn't be like the minutes of an actual meeting.