Having worked with big iron for several decades, I am not impressed. Microprocessor based systems have been just as reliable and effective, and, yes, I have personally built as large, scalable, and high performance database systems as anything I have worked on for a mainframe. I am not impressed with IBM in any way. It is jsut another large corporation where the execs don’t even know what they sell.
Even people I know who have jumped to ORACLE clustered systems don't claim that its more reliable than a Power system on the I OS.