digitalrampage, a LOT is going to need to happen with drive technology to get a laptop drive over 60GB AND maintain the current thickness of them. While it will [eventually] happen, I wouldn't dream of assuming it will be done in the next 3-4 years. Look at it this way, IBM had to advance the platter design, and process, to get the 60GB drive (12.5mm thick). That does fit inside the TiBook, but it doesn't leave all that much room to spare. To maintain that as a maximum thickness, they are going to have to increase the platter density, since they will not be able to increase the number of platters much (if at all).
Look at how long 120GB and 160GB 3.5" drives have been out. There has yet to be an increase in those beyond the 160GB mark (yet at least). I am sure the drives are being developed, but who knows what kind of hurdles they have to get over before actually starting to produce them. That is, except for the people actually on the design teams.
Over the next few years, I can see drives (3.5") getting up into the hundreds of GB in size. They very well could grow in height to get there though. That is not an acceptable sacrifice for laptops, since drive thickness is a critical issue.