I have been thinking about this a lot as I look for another position. I have always been the "glue" person at my current work so things would be rocky for a while if/when I leave - but probably not for long. Additionally, I have a lot of historical knowledge having worked for the organization since its inception. Not sure that matters anymore though. I really like the sense of contributing to an effort and where I am now is feeling less and less fulfilling. Assuming you work for someone else, would they miss your presence if you moved on or are you easily replaceable?