(I don't care about this Bear analytics thing at all, and just clicked the comment thread to see if it was the Bear I thought it was; I do care about people's misconceptions about hashing.)
The only thing you can brute force from that is some IP and some salt such that SHA1(IP+Salt) = 6FF6BA399B75F5698CEEDB2B1716C46D12C28DF5 But you'll find millions of such IPs. Perhaps all possible IP's will work with some salt, and give that hash. It's not revealing my IP even if you manage to find a match?
Yes if all you ever want to send is a unique visitor ID then there is no point in having a local hash, because you can just generate a random ID and use that to identify the user.
What I mean is that if you want to send multiple pieces of PII (such as an IP, a filename, a username,...) then the only way to do that safely is to send hash(salt+filename) for example, where the salt is not known to the server receiving the hash. The IP in the suggestion to use a locally stored hash here just represented "PII that should be sent anonymously" and not "A good way of identifying a unique system".
Sure, but it does at least prevent the use of rainbow tables. Arguably not relevant in this scenario, but it doesn't mean that salting does nothing. Rainbow tables can speed up attacks by many orders of magnitude. Salting may not prevent each individual password from being brute forced, but for most attackers, it probably will prevent your entire database from being compromised due to the amount of computation required.
"Salted hashes" are one of the more treacherous security cargo cults, because they create the impression that the big problem you have to solve hashing a password is somehow mixing in a salt. No: just doing that by itself doesn't accomplish anything meaningful at all.