Linux 2.6.6 was released recently, and there looked to be some interesting enhancements included. The first thing that caught my eye was the option for a 4KiB stack instead of 8KiB. This is designed specifically for machines running a large number of threads, which is common with java app servers. I can't say I've noticed anything too different here, though. Maybe my long-term swap usage will be lower with my JBoss server running. It's still occupying the usual ~300MiB of virtual memory.
The surprise feature is that laptop mode has been merged into the kernel. I had looked at this patch previously, but my laptop didn't really give it a chance to spin down the drive. It actually seems to work these days, and it can spend a considerable amount of time spun down.
Update (19 May 2004): It seems that the native FIR IRDA driver (smcc_ircc) is magically now working and finding the right base I I/O addresses. I'll have to see if it might communicate faster with my phone now.