I thought seriously about it around ten years ago. I decided to stick in out in my current field because I do still enjoy it as a whole. The real deciding factor for me was the experiences of two of my brothers who attempted mid-career changes. Both, because of circumstances beyond their control, ended up being unemployed or underemployed for quite some time. It wreaked havoc on their finances and families. Fortunately, they both have managed to get back on their feet but it cost them. In this economic climate, with jobs so scarce and new employees being the first to be shown the door during cutbacks, I wouldn't even consider a career change unless I was absolutely miserable where i was.