I think part of what we (anyone with an idea or an entrepreneurial urge) miss is: if an idea is marketable, there’s room for competition. There very fact that competition exists is a good thing - it proves that a market exists.
In some cases, competition can even simplify your plan; find out what your competition is doing wrong (or could be doing better), and do it right.
A local example might illustrate what Aiken’s quote means to me: Here in Minneapolis there is a fast growing local coffee chain called Dunn Bros. Coffee. How could they — or anyone — even try to compete against giants like Starbucks? Automatic “bad idea”?

As it turns out, no. Dunn Bros sells only coffee roasted fresh in the last few days, and most locations feature local artists’ work on the walls. To a coffee lover or a person with a soft spot for local artists, it’s automatically better and hipper than any Starbucks could be or probably ever will be.
(Okay, it’s pretty easy to see which place I prefer. Actually, some of the independent coffee shops here are very good as well, but they don’t make as good of an example.)
That said, if someone came up to you and said, “I’m going to start a chain of coffee shops and compete with Starbucks/etc” — sounds like a pretty bad idea. You would literally have to ram it down peoples throats to get them to see that it could be done, and they still might not see it.
Is there any competition too big? Microsoft? Google? IBM? Maybe, in some time periods, and for awhile. But Microsoft pulled the rug from under IBM, and Google seems to be doing the same to Microsoft. Eventually someone will do it to Google, and who’s to say that it won’t be you? That sounds a bit crazy — and certainly I don’t think that any of my ideas from the previous post are in the “Google-killer” category. But the point is, if you decide before you start that you can’t compete with company x, you’ll never start. And the company who does become the New Leader in their field will do so despite everyone who told them it couldn’t be done.
Another of my favorite quotes, when applied to business or competition:
“If anything in this life is certain, if history has taught us anything, it is that you can kill anyone.”
- Michael Corleone, The Godfather: Part II (mp3)
EDIT: And yes, that is my sorry attempt at a Kathy Sierra style funky illustrative graph. I try.

I think that the Google/MS thing is significantly different to the IBM/MS thing. Google are, so far, the best in a very competitive market, but they stay ahead by being consistently better, and by constantly innovating and expanding.
I think you’re correct about Google/MS being a different situation. It’s extremely different. I guess my only point was that no one, no matter how huge, is immune to competition.
The MS/IBM deal was a combination on some prescient foresight on Microsoft’s part, and a lack of the same from IBM. Alternately, it could be viewed as a really underhanded move by MS — depends on whether or not we’re talking about msdos or os/2-windows. Either way, I agree — completely different situation.
Only common denominator; no one is immune.
That said, IBM having changed their main focus to services and consulting really seems to be working out well.