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Update 8/14/2012 - Found what appears to be a better configuration. Please note, I'm no expert at this. It's been a matter of trial and error and a bit of google. So, do this at your own risk. But, seems to be working well. This was the most useful guide I've found so far related to this.

http://panoramicsolution.com/blog/?p=388

Since everything now seems to "just work," I will leave it as is. But, I plan to learn more about what exactly all these options mean in greater detail over time. Specifically those defined in ifcfg-eth0/1 and ifcfg-bond0.
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The how-to for COS 5.x is here, but a few pieces have changed in 6.3.0
http://www.clearfoundation.com/docs/howtos/network_bonding

I wasn't able to find a 6.3.0 guide anywhere else in the forums, so here is what I did to get 2 NICs bonded in 6.3.0.
Not sure if it’s ideal, but it did work.
This guide is really just a summary that may help some get started.
Any input or suggestions would be greatly appreciated.
Still not 100% clear on what the potential maximum throughput is in this configuration.
If nothing else, you get redundancy.
And, of course, I copied all the files I modified to my home folder before making changes.

This guide bonds eth0 and eth1 to bond0 and assumes you are familiar with the CLI and have root access to the machine.

Ensure bridge-utils is installed.

yum install bridge-utils

Create /etc/modprobe.d/bonding.conf if it doesn't already exist and add the following.

alias netdev-bond0 bonding

Modify /etc/sysconfig/network-scripts/ifcfg-eth0 to the following, of course, matching your network configuration.

DEVICE="eth0"

NM_CONTROLLED="no"

ONBOOT=yes

TYPE=Ethernet

BOOTPROTO=none

DEFROUTE=yes

PEERDNS=yes

PEERROUTES=yes

IPV4_FAILURE_FATAL=no

NAME="System eth0"

SLAVE=yes

MASTER=bond0

Modify /etc/sysconfig/network-scripts/ifcfg-eth1 to the following, of course, matching your network configuration.

DEVICE="eth1"

NM_CONTROLLED="no"

ONBOOT=yes

TYPE=Ethernet

BOOTPROTO=none

DEFROUTE=yes

PEERDNS=yes

PEERROUTES=yes

IPV4_FAILURE_FATAL=no

NAME="System eth1"

SLAVE=yes

MASTER=bond0

Create /etc/sysconfig/network-scripts/ifcfg-bond0, of course, using a valid, available IP address on your network for the IPADDR.

DEVICE="bond0"

ONBOOT=yes

BOOTPROTO=none

IPADDR=172.16.8.15

NETMASK=255.255.255.0

GATEWAY=172.16.8.1

NAME="bond0"

BONDING_OPTS="mode=6 miimon=100"

I modified the beginning of /etc/clearos/network.conf as follows. Different setups my require different configuration here. Not really sure. In my case, this machine is simply a file server/NFS server/soon to be minidlna server on my network.

# Network interface roles

EXTIF="bond0"

LANIF=""

DMZIF=""

HOTIF=""

Reboot (I'm sure there is a better way, but a reboot works just fine.)

In the webconfig, navigate to Network | IP Settings.
Under DNS, ensure there is a valid DNS server IP (in my case, 172.16.8.1, the IP of my ClearOS gateway.)

That should do it.
I have no idea if future updates pushed out by ClearFoundation may replace/modify any of these files... thus causing the customization to be lost. But, that keeps it exciting.