I am doing pretty much the same thing, transferring all data from early 2008 MacBook Pro to similar but newer model with more memory, larger HDD, other upgrades, running Lion instead of Snow Leopard. The Lion Setup Assistant and Snow Leopard Migration Assistant steer the user to wi-fi by asking how you're connected to the Internet. Even though I plugged in a CAT5 ethernet cable AND a Firewire cable directly between the two machines (to let the Macs choose), the transfer of +/- 200 GB was going to take 15 hours, and the count was going up every minute or so, not down. I'm pretty sure the Macs were ignoring the hard-wire connections and using the wi-fi I had identified when asked. I stopped the transfer (had to turn off the new machine, as there was no Cancel option) and started over. But this time, I disconnected the wi-fi network and told both machines I wasn't connected to the Internet. Once transfer began this time, it said the process would take 51 minutes, and while I was reading these posts and writing this message, it's down to 28 minutes. Conclusion: Don't let the Assistant sucker you into using wi-fi.
Mputzel -- Excellent point. It would be valuable for the MA prompts to tell users to shut off WiFi before attempting to use a hardwared transfer. Your comment brought my transfer time from 25 hours to 1.5 hours. Oddly, the Thunderbolt connections were not recognized so I needed to use Ethernet. Thank you.