*** Update 10/26/09 ***
Free is Back!!
Well it never really went away, but not its easy to run the free version of splunk.

Downloads still contain an enterprise 60 day license, but you can covert to the free product at time you like and use it like a champion.

Back several months, before the launch of 4.0, we were confronting at all the work ahead. As always, we had to make hard decisions about what is in and what is out. In 4.0 we had re-implemented much of the UI and a good chunks of the backend. With over 1000 paying customers and looking at a potentially challenging upgrade process and a huge testing task we needed to reduce risk to the schedule and product quality. It was a hard decision but we reduced the GA risk by pulling out the Free product until we GA’d and fixed most of the critical bugs. Our guess was that it would take 45-90 beyond the GA to get few maintenance releases out before we could test the free product.