Many times I have heard this verse used as justification for modern-day pastors earning salaries from their churches. This verse is applied directly to them because, they reason, they "proclaim the gospel."
However, the reality is that this passage does not apply whatsoever to pastors. Nowhere in this verse or the entire passage does Paul even mention elders, overseers, or pastors. Simply put, elders do not appear here (read I Corinthians 9 here).
Paul is discussing those who travel from location to location proclaiming the gospel. He seems to have apostolic workers and evangelists in mind. Since they travel around, they need financial support. Elders, however, since they come from local congregations where they live, do not need this support since they can have regular jobs.
We should also keep the broader context in mind when studying this passage. Paul is discussing the issue of Christian liberty. Paul is not willing to use this liberty, as it relates to receiving financial support from the Corinthians, because he does not want it to in any way hinder his proclamation of the gospel.
We do know that Paul received financial support from the Philippian church, thus showing that it was acceptable for apostolic workers to do so.
Back to the issue of elders. In the end we must come to the conclusion that when Paul wrote this passage, he did not have elders/overseers/pastors in mind. The context excludes them altogether. Therefore, this verse should not be used to justify modern pastors receiving any sort of financial support.
(There is another passage pertaining directly to elders which is used by many to support pastoral salaries. That passage is I Timothy 5:17-18. I'm going to address those verses in a later post.)