I've been in IT since 1990. Hmm - that's 15+ years.
First started doing systems assurance/QA/scheduling on mainframe sysetms. Shortly thereafter, I moved into storage management, and have been in storage since then.
I have been very satisfied with my career thus far. The key to my satisfaction is that my position has evolved from just a mainframe storage guy to a SAN (storage area network) administrator where I single handedly manage about 30 TB of storage for not just the mainframe, but open systems (UNIX & Windows) systems as well. I also manage the switches/directors on the SAN fabrics.
And the cool thing is that even SAN systems are evolving with stuff like virtualization, newer infastructures, newer DASD - so I'm constantly learning about new hardware/software and theories and trends. Keeps me on my toes.
Oh, and since working for Mercedes-Benz, USA, I've also been responsible for the mainframe disaster recovery processes, and I've got my fingers in change control and daily operations too.
Bottom line: so far, my field has been constantly evolving and expanding - without those, I'd be looking for a career change.
Just my personal experience,
-Zoltan.