Ever since I wrote the initial essay about mesofacts, a great number of people have been telling me that the height of Mt. Everest is itself a mesofact. After consultation with a number of people, including a geophysicist, here's my update:

First of all, there are a few aspects to deal with: the heights that people have recorded have changed simply due the change in the precision of our instruments, but now that our measurements are quite precise, we also know that the height of the mountain actually does change a bit every year.

In terms of measurement error, here is a good example: "The observations made in 1954 varied by 17 feet; the margin of error in the 1999 calculation was only a fraction of that."

In terms of the actual height, It seems that there are two competing forces. On the one hand, the collision of two continental plates (Asia and India) causes a certain amount of uplift each year (perhaps about a centimeter or so per year, although there seems to be some disagreement). On the other hand, other forces, such as erosion and melting glaciers can cause a decrease in height (see here and here). So, it's unclear how much it changes each year, although the height is never exactly constant.

Ultimately though, it's a matter of scale. If the height of Mt. Everest is the same, rounded to the nearest foot (or whatever your unit of choice is), for hundreds of years, some would say we can count this a long-term fact. While it's probably not true for Mt. Everest, perhaps it's more accurate to say that the fact that Mt. Everest is the tallest mountain is a long-term fact (though we have only known this for a hundred and fifty years or so), while it's height is a mesofact. Apparently though, Mt. Everest is moving laterally at quite a nice clip: 6 centimeters per year, so it's location is also a mesofact.

(thanks to everyone for feedback on this)
The cost of U.S. stamp has changed over time. While you can download the USPS raw data, I actually just found most of this data on Swivel, a wonderful website for manipulating and visualizing data. I highly recommend checking it out.
The mean center of population has been calculated for every census since 1790. In addition, you can do the same calculation for a single city and see where its center has shifted. For example, here's an article that discusses this in New Orleans (thanks to Mary Beth Magee).
How do you deal with a nosebleed? For a long time, the state of the art was to lean your head back, and that is what I am sure many of you learned when you were younger. Well, it’s not a good idea and can apparently cause you to choke on your own blood. You’re now supposed to pinch below the bridge of the nose and hold (with some slight leaning forward).
This shows the total number of nucleotides (letters of DNA) that have been registered in GenBank, a national repository. The data is from GenBank (visualized by some Wikipedians). Then number of nucleotides is graphed on a logarithmic scale, where a straight line means that the number of nucleotides that have been registered is increasing exponentially.
This shows the cost of living in the U.S. over time. More visualizations of economic quantities over time can be found at Visualizing Economics.
As an example of university donations, this displays the change in cash gift amounts for Cornell University from individuals in recent decade, even though the amounts from foundations and corporations has remained relatively constant.
Membership in the United Nations, over time (graph produced by Samuel Arbesman from U.N. data). Please contact us if you would like the dataset.
The world record progression in the Men's 100 meter dash.