I own both devices, so I'll give you the skinny.
I don't like the Touch. I'm not sure what it is, but the more I use it, the more I see it as a step backwards from what a full laptop can do. Granted, that's not what it's meant for, but all the same, why carry two full-blown computers when one is all you need? I've been pairing the iBook with either my first or third generation Nano, and it's been a pretty good on-the-go setup.
It depends on what you want to do with the machine. I'm still of the opinion that if I'm going to take a computer with me, it needs to be able to be an email reader, web browser, word processor, iPod, instant messenger, photo repository, and a bed for running applications. Some of these things are difficult nigh impossible on the Touch, and even on an iPad.
That being said, if you want acceptable battery life or access to online video, the Touch is a much smaller, cheaper option than upgrading a 10 year old laptop. I've loaded my Clamshell to the gills (and it will be getting a new high-cap battery for school), but I've done so because I'm willing to live with it's limitations because I love it's aesthetic and it does all I need.
In a nutshell, yes, a Touch is more powerful. I think the jury is still out on "more usable", however.