Yes! Despite all the things you have heard, the
mainframe, that kind of Behemoth computer, is still alive and
kicking.!
Since 1992, I earn my live programming for 'la Caixa' dealing with those IBM monsters. I use the PL/1 programming language and deal with IMS/DB and DB2 databases.
Previously, I worked with DEC's VAX/VMS for four years. I did System Manager and programming tasks. VAXes are not strictly mainframes, but they share with them the concepts of robustness, high workload support and timesharing.
A guy named Eric Loriaux has built a nice WWW page devoted to the MVS/ESA environment. If you are a mainframer or are curious about mainframes, visit it and drop a line for Eric. He is doing a great job putting together all that mainframe stuff.
Some links about mainframing: