signifanctly slowdown of FreeBSD 8.0-CURRENT/amd64

Hello.
I realized a significant slowdown of FreeBSD 8.0-CURRENT/amd64 on every
box I run. I have the most recent FreeBSD 8.0-CURRENT/amd64 with custom
kernel and switched off every debugging. I see a drastic slowdown
whenever heavy I/O on UFS2 and ZFS partitions is performed and whenever
some compilation is done (compiling world and kernel). This is horrible
on a single core Athlon64 CPU with 2GB RAM as well as on a 4 core Q6600
with 8GB and a server with 2 x 4-cores and 16GB RAM.

I can not say clearly whether I/O is the bottleneck. Maybe something
with the memory subsystem, when it comes to compiler runs, when no disk
I/O is done but the box is still horrible slow. This behaviour occured
several weeks ago, not being able to specify it more precisely.

AQre there any issues at the moment?

Thanks for answering,
Oliver