My profile on careers.stackoverflow.com used to have a part where you could highlight top tags, i.e. it would something like along the lines of Top % for [TAG]. That doesn't seem to be showing today however, so has this been removed?
The criteria for a tag to be available on Careers 2.0 top percentiles is that it must have at least 500 total answers by users that have at least 2 answers and at least 20 total upvotes in the tag. The real kicker is that all of these eligible people must also have an account on Careers 2.0.
The reason we rate the tags only against members of Careers 2.0 is that SO has a long tail of people who have answered one question in a tag because the question wasn't really about that, or the question could be answered by someone who is not particularly familiar with that technology. We try to give the rating not against everyone but only against people who appear to have some actual knowledge about the topic.
Currently the salesforce tag has only 470 eligible answers on Careers. As soon as it gains the required number of answers, you will likely go from nothing to top 10%. This exact thing happened to me on the web-development tag. As for this showing up previously and then disappearing, this is likely due to our account merging process which is being updated later this week.