The rapture is just one event that we try to put on the timeline. If it is at the beginning of the tribulation, then it becomes imminent when the tribulation becomes imminent. We are not there yet.
There are a number of things that I have been watching all my life. The events surrounding Israel are truly awesome, but the prophetic puzzle pieces are not coming together as fast as I would like them to. The last event that I think is a specific event in prophecy is the possession of Jerusalem by Israel. That will be 40 years ago, come June.
Not all teachers of prophecy have taught that the rapture is imminent and I still do not think that it is imminent. I will admit that it is a position that is increasingly difficult to defend.
It certainly is closer today then yesterday.
What it really does when it happens, is start the prophetic clock of the last week of Daniel's 70th week going again, a clock that has been 'stopped' during the Church Age.