So I am not alone. I too have been using the vi/command-line development suite for as long as I can remember. There are a few reasons for my use of vi/command-line development (and not just for Perl).
First, is just as you said, there is a necessary time period needed to familiarize yourself with a new programming environemnt. With my current development habits, I can go from language to language with no need to spend time on learning the interface. In my opinion, this also lets me focus more on the code that I'm writing and not on looking for the "Compile" button.
Secondly, it helps when working on older systems. I know that everyone has got an old clunker that they have to work on at some point as part of their job, and an IDE would floor the system. The combination of vi/command-line lets me get my work done and not kill the system in the process.
Another reason that I have shied away from IDE's is horrible error messages. I have found that some suites simplify/group errors into generic messages that often make debugging difficult. For example, Borland started using the "Error: Thread stopped." (or something to that effect) a little too much to be useful. You'd get that error if you overstepped memory bounds, used the incorrect type, or even if the server handing out the headers was being stubborn.
I personally don't see myself changing how I develop in the near future. I plan to keep on using vi as my development suite for years to come.
If the world is to end in a whisper, I hope that it's not someone whispering,"I wonder what this button does?" -DTB