I agree, 25MB per second is hella fast over the network. I bet you are slowed down by your hard drive. unless you are using RAID with multiple drives your not going to get much over 25 or 30 MB/sec sustained.
As an example, I have a P4 2Ghz workstation running FC2 with a 7200 RPM IDE drive.
here is my hdparm -t /dev/hda output
[root@avod-sandej-lx mnt]# /sbin/hdparm -t /dev/hda
Timing buffered disk reads: 128 MB in 3.03 seconds = 42.25 MB/sec
I'm peaking at 45 MB/sec just inside the box getting to the hard drive. Throw in going over the NIC as well and I bet I would peak around what you are getting with gigabit networking.
Try running that hdparm test on your drives and see what the max performance your drive is even capable of and you might begin to feel better about your network speed. Heck, your connection between systems is faster then most peoples directly connected hard drives!