A direct comparison between Vannevar Bush's "As we may think" and Kevin Kelly's "The next 5,000 days of the Internet", is the references to the "machine". Bush refers to it as a "piece of furniture" which stores a collection of scattered knowledge within it. Kelly's vision of the machine, while similar to Bush's is a little more specific considering it was discussed in a time when the technology they referred to has already been invented. Kelly's reference to the machine is the most perfect machine to ever be made, constructed through the consumers; the users of technology through cell phones, computers and any other handheld devices.
Regardless of their depth in explanation, both men's ideas about this machine are very similar. The way that I interpreted the idea is that basically even though as humans we are doing exceptionally well keeping up with all the new technologies, it is eventually going to catch up with us unless we have one solid center to bring everything together so we can keep it under control and managable. An example of this, on a very small scale, it is the equivalent of having widgets on our webpages, so that all the sites we constantly visit can all be organized in one little spot.
I honestly did not see any noteable differences between the two ideas. The only point I think is worth mentioning is that Bush's ideas were predictions (which ultimatly had truth) and Kelly's ideas were based on facts from the previous 5,000 days. I think they were both right and it is only a matter of time before we create new forms of technology to put into the machine.