The famed webOS Internals group has created a historical adoption graph for webOS using registration data collected from users. According to their findings, roughly 4.2 million webOS profiles have been registered, with a significant uptick around the time of the TouchPad fire sale. The graph is made possible with very little data because each webOS user must create a profile with Palm and each one of those profiles gets assigned a number in an ascending sequence. The team asked users to report their profile number (which is visible in the homebrew application Impostah) and registration date and used the highest number reported for each date as the number of profiles created at that time.
The numbers might not accurately reflect the size of the active webOS community because each phone requires a unique profile, and some users have stopped using webOS. However, because the same profile can be used for a phone and a tablet, the increase around the fire sale could indicate that many TouchPad buyers were also new to webOS. The data isn't verifed by HP, but it still provides some insight into the user base of the seemingly-doomed OS. If you haven't already done it, download Impostah to reveal your profile ID, and add your data to the Google doc at the source.