Yes, people are installing the software OK and it sounds from the message like you have a damaged copy. This was probably caused by the server being so busy with everyone trying to download the software at the same time.
I, too, have been experiencing this error. Multiple times, and after multiple downloads.
I tried downloading twice via Firefox, and after the second install fail, I commented (politely, although mildly frustrated) about it on Twitter. @ESLightworks replied, and suggested another browser.
Tried Chrome instead. Full download, error on run.
So I also tried most of the steps on http://nsis.sourceforge.net/NSIS_Error, from the section "If the software was obtained from the Internet", re-downloading almost every time. Some of the steps I couldn't do:
#7 because I tried to download via another computer (using first IE *shudder* and then Firefox), and the download stopped, "complete", at 87MB. I didn't bother trying to copy them across, so I therefore didn't run them.
#8 because I don't have the nVIDIA firewall.
#11 (wasn't necessary).
So, I've downloaded the installer seven or eight times, and every attempt at running it (including one where I ran it as administrator) resulted in the NSIS error. I didn't want to risk the steps in the "Final Options" part of the NSIS page.
My system: Windows 7 Ultimate 64-bit, 2GB RAM, two 140GB hard disks.
My download was kicking out after only getting part of the file (~50 MB instead of ~136 or whatever it should be) and I got the same error when trying to install.
I solved it by downloading from a faster connection at work, so it got the whole file before kicking out. I know that doesn't help you much. Maybe try again after the initial rush dies down.