"Legacy applications are old. But how old? I tend to think of my VB6 apps as legacy. But heck, they are modern compared to another app I have hanging around. I have avoided accepting the fact that I was working with an application that was at least 16 years old. The oldest file I can find in there is from early 1991."
Source: Julie Lerman
It's always hard to decide when it's time to re-write those legacy apps. The decision, for us, was easy. We had a 15+ year old COBOL application installed on a number of customer sites, these customers were starting to get really picky. I mean, they were looking for stuff like multiple windows, and right click menus etc, can you imagine! The cheek of it. Anyway, it became pretty apparent that the old system needed to go, and so we decided we'd replace it. We changed the old, monolithic, flat file based system, with a modern, 3 teir .Net application based on SaaS principles. If you want to know how we did it, check out the project page here.