SimilarWeb has a nice compare and contrast feature so you can track monthly visits to two different sites, and as you can see above, Sansar.com and HighFidelity.com are definitely gaining interest - up to 151K and 61K visits, respectively, last month. "Visits" are not the same as unique users, and a pretty good rule of thumb is to assume ~5 visits per actual person. (Since a single visitor is usual clicking on images and other links on the site which might also be recorded as "visits"). So on that logic, an educated guess is in July, around 12,000 people visited High Fidelity, while 30,000 people visited the Sansar page. No surprise there, as Sansar's open beta, widely covered in the tech and gaming media, was last month. Site visitors, of course, are not the same as people who actually created a user account, downloaded the client, and actually visited the world. A good rough guess is 10-20% of visitors did that in July -- i.e. low to mid-thousands.
By contrast, compare Sansar.com visits with SecondLife.com visits:
22 million visits to SecondLife.com last month. We know monthly users of Second Life are around 900,000, a lot of whom use the official portal to access their account, buy/sell Linden Dollars, etc, which is going to increase average "visits" way more than 5x per person. In any case, it's likely quite a few non-users are still hitting the site too!