What the IBM 5100 really represents, in retrospect, is the beginning of the turnaround for IBM in the minds of the public. It's difficult to think of another example of a company so large and so universally despised eventually becoming the (mostly) developer friendly company it is today.
By allowing their teams to skirt the system occasionally, we've seen truly open hardware (PowerPC) availablity, open source contributions, free training seminars for developers, etc. The 5100 was the first great example of the success that a little rule-breaking can bring to the company.
IMO, it was exactly that product and the example that it was to IBM internally that allowed IBM to do the one thing no one was entirely sure it would be able to do in the age of personal computers -- survive.
My hat's off to the improvements IBM has made in the last 25 years, and I hope that those lessons won't be forgotten over the next 25 years.