This subject is slightly more controversial than my usual writings, and I do not really have any hard evidence to support my view here, and in some cases the myth is not really a myth, but I really think that in many cases this myth is just that, an exaggeration and false memories people have.
The myth is the following: Even though computers have gotten faster and faster over the years, software (such as for example MS Word) has not, and the software is nowadays as slow as, if not even slower than it was over ten years ago. Performing the same basic tasks with current hardware and software is as slow, if not even slower, than it was over ten years ago.
Basically this is the notion most people have that modern software has gotten so bloated that running it is as slow as, or even slower than running the equivalent software over ten years ago with computers of that era. Many people complain about this, and you see people reciting this claim again and again.
However, this notion is just a myth. It's not true.
Now, don't get me wrong: In some cases it is indeed true: A modern version of a certain software may indeed be slower in modern computers than very old versions were in computers of the era. However, what I'm saying is that this is more an exception than the rule. The notion that software in general is nowadays as slow as it was over ten years ago is just a misguided myth without any basis.
Usually when someone recites this myth and you ask for concrete evidence, hard numbers, anything, they fail to provide any. People rely solely on their own faint memories of what it was to use computers over ten years ago. These faint memories are colored by hearing this myth over and over to the point that people start believing it without questioning it. In some cases people even may start forming false memories based on believing this myth. They might remember the software indeed feeling faster over then years ago than it feels now.
The fact, however, is that nowadays software is in general vastly faster than it was over ten years ago.
One thing which partially strengthens the myth is that nowadays the software tends to do more than its ancient version did, which causes it to not to work in general as many times faster as the computer is faster. However, there just isn't hard evidence that the software is actually performing the same tasks as slowly as its ancient version did in the hardware of the era.
On the contrary, most tasks are nowadays considerably faster than they were back then.
Want to open a 6000x4000 pixels large image in an image editing software? That usually happens in a split second, while in the old hardware it may have taken tens of seconds, if not even minutes to open. Want to make some modifications to that image (such as applying some filter)? Again, a matter of at most a few seconds, while the old hardware would have taken much, much longer.
Want to browse the internet with a web browser in your 1600x1200 pixels display? Quite fast and light. Over 10 years ago web browsers were sluggish even on tiny 800x600 pixel displays.
Video editing? You could only dream about being able to do that over ten years ago. Nowadays it isn't even a problem. Playing some high resolution videos? Nowadays the CPU doesn't even get warm with them, while over ten years ago you were lucky if you were able to play it at all.
Many people will argue that "ok, maybe things requiring heavy calculations run faster nowadays, but what about things which don't, like text editing?" Yet they usually fail to show any concrete evidence to corroborate that things like text editing is now as slow of a process as it was over ten years ago (unless, of course, the writing speed of the person has not improved in the meantime, but that's not the point here, of course). Many people claim that things like editing text has become slow in current computers, but I believe that in most cases it's simply a question of false memories: They don't remember anymore how sluggish the text editors were back then.
As I said, sure: Maybe a few things might take slightly longer today than they took over ten years ago. However, these are just a few exceptions. The general trend is undeniably that software today works tremendously faster than software in the past. What we are talking is the mistaken notion that software in general is today as slow, if not slower, as it was in the distant past.
There simply isn't anything which would corroborate this claim. It's just a myth.
Another point is that often people compare apples with oranges here. Even though a software may have the same name as a much older software (let's say, for example, "MS Word"), that doesn't mean that hey are the same software. People are comparing two completely different programs. The problem is that the newer program is doing more than the old one.
To put this into perspective, consider this: Playing, for example, Half-Life 2 in a 2GHz Pentium4 may be as slow as playing Doom in a 33MHz 486 with regard to framerate. However, this is comparing apples to oranges. The comparison is completely unfair and out of place. This is because Half-Life 2 is doing a lot more than Doom. They are not doing the same thing. The only thing common in both programs is that they are both first-person shooters, but that's it.