I don't claim to be an average user, but what I want to do is compile things. Now that LFS is stable enough to run tests over long periods of time, I've been able to park a machine under my desk building releases over and over; here are the results.
The following table lists the time in seconds spent building the NetBSD 1.6 release (not counting any time taken to unpack the sources):
FFS has an average build time of 37907 seconds, and LFS an average build time of 35913 seconds; a savings of just over 5%. (Note that this is 5% of the total time; I expect a build to be CPU-limited rather than filesystem-limited!) The FFS in this example is NetBSD 1.6 FFS, mounted with softdep, bsize=8192, fsize=8192, cpg=69. The LFS likewise has bsize=fsize=8192, with sgs=7. The filesystem grew to be about 70% full over the course of the test; the cleaner was running.
The script used to generate these results is here. The configuration of the machine, and a sample df are here.