RPCPROG_MNT: RPC: Timed out / receiving NFS error when trying to mount NFS file system after make world

Hello,
since today I get this error when trying to mount a NFS filesystem from 
NFS server:

[udp] foo:/home: RPCPROG_MNT: RPC: Timed out

Both boxes, cleint and server, are most recent FreeBSD 8.0-CURRENT/amd64 
from today's buildworld/make kernel.

nfsd is up and running and worked that way days before.

I saw commitments of new NFSv4 code, are these causing this issue? Is 
8.0 supposed to be offering nfsv4-server capabilities which I need to 
switch on anyway?

I also tried mount -t newnfs on that NFS filesystem but without any 
success. Is this a fault of mine or are temporarely not-working-condition?

I tried both ZFS and UFS2 NFS exports to get mounted, both are unwilling 
to mount with the above showed error.

Regards,
Oliver