Slow transfer between iMac and Macbook Pro
To transfer via FireWire, turn off one of the Macs, then when powering it on hold down the 'T' key. This will put the computer in Target Disk Mode and make that computer's disk available to the other computer. You can then just drag and drop between the two drives on the other computer.

If you connect the cable when both computers are powered on, your Macs will treat it like a network, assign themselves IP addresses, and use Bonjour to broadcast their sharing services. You will be able to connect via AFP/SMB/etc, but this configuration defeats the purpose of the firewire cable - you could just get a cat5e or cat6 ethernet cable and make the same connection, and it would be faster than Firewire in this case (assuming both Macs have gigabit ethernet ports)