I did some number-crunching after purchasing a few keywords and "scoring" my words against the search word "porn" on "google trends". My words scored over 700% of total searches for "porn", per month (774% to be exact).
At 33.34 Satoshi per one of my keywords being searched (I divided 100 satoshi by 3, as I figure searches will probably average 3 keywords), and figuring that there are 100,000 users per month on the searchtrade search engine, each averaging about 6.667 searches, my list of keywords generated only about 0.0171 BTC after one year.
So, according to my calculations, unless the value of Bitcoin shoots through the roof (over $10,000 per Bitcoin...staying there), searchtrade's search engine must achieve 10 million users per month, or more, to be profitable to the community pool (keyword owners).
At 10,000,000 users (or 66.67 million searches) per month, my keyword list would generate about 1.71 BTC per year, meaning that the word "porn" would generate 1.71 BTC divided by 7.74, or 0.221 BTC per year ($50.35 per year at Bitcoin's current price), since my list is projected to generate 774% of "porn" searches - this all assuming the same distribution of search "habits" for visitors between searchtrade's search engine and Google's.
BTW, there are roughly 5.8 billion searches per day on Google's search engine. This would likely equate to around 870 million users of the Google search engine per day, using the same math from earlier (total searches/ 6.667 searches per user = number of users).
This is valuable information to have as an investor in this, which is why I chose to share it here.
*edit:
Another bit of interesting info for you: this same list of keywords would generate about 12.26 BTC per day on Google's search engine, at 1,103,172,409 searches per month for my keywords! I wouldn't mind it if searchtrade could grow to that size...
*edit 2:
I likely used a low-ball figure for the number of searches for the word "porn", per month. According to "google adwords", the word "porn" is searched about 124 million times per month, currently. Since "porn" scores an 87 at the moment on "google trends", when it was at its peak (100) it would have been searched about 142.5 million times per month (assuming the google adwords estimate is reliable).
The problem with using google adwords is that, I believe, it only counts how many times the word is searched, alone (without other words included in the search query...so, for instance, the search "hot porn" wouldn't count as a search for "porn", since another word is included) ...which would likely make this a VERY low-ball figure.
But even if the word "porn" is searched ten times as often as google adwords suggests, putting the total searches per month at 1.24 billion, 1.42 billion at its peak, it would still only generate about 0.0244 BTC per year for the word "porn", at 667,000 searches per month (what I figured to be the number of searches for 100,000 users).
The planned payout system requires that there be tens of millions of searches per month for this to become profitable. At hundreds of millions of searches per month it would become very attractive for those who hold keywords that generate a high number of searches relative to the pool of keywords (words like "the", "porn", "sex", "facebook", "youtube", etc). At billions of searches per month, if Bitcoin can maintain above $200, this might be able to replace your job for income with a high scoring word and give a decent yearly profit for even average scoring words. At tens of billions of searches per month, one can retire and live beyond his/her means with a high scoring word and perhaps replace their job's income with one or two average scoring words. At hundreds of billions, you might make it onto Forbes magazine with the highest scoring words!