I was able to fix the problem on my own. The performance problems without a doubt are related to the specific version of samba that comes with the default firmware. The firmware samba version is 3.0.28. I installed the ffp version of samba version 3.3.2. The difference is night and day. Transfers went from 4-5MB/s to >8MB/s on 10/100 ethernet. That's a 50-60% improvement. I wish DLink would get on the ball and update the official firmware with the updated software and add telnet and rsync while they're at it. Their support has been beyond worthless.
Here's my ffp samba section:
echo "* Disabling samba 3.0.28 ..."
smb stop
echo "* Loading samba 3.3.2 ..."
/ffp/sbin/smbd -s /etc/samba/smb.conf --smb-passwd-file=/etc/samba/smbpasswd
echo "* OK"
This allows you to use the configuration file from the web. However, I'm pretty sure you have to reboot to get it to take effect since the web config launches the old config script. I'm sure you could modify the "smb" script to fix this as well.