We use the AS400 / iSeries / IBM Power Server running i5/OS for our financials, customer service call center, claim processing, time and attendance, collections, sales analysis and profitability, sales contact tracking (CRM), and online transaction processing for our customers. We have two small iSeries, Power 5 - 520's that are dedicated to OLTP. One in our corporate data center and one in our remote data center. These are both mirrored via Data Queues, ICF, and journaling along with our back office system, a power 7 720.
The back office system is the one that all the employees use daily. This power 7 720 is mirrored via Mimix to a power 6 520 in our remote data center.
We have about 250 interactive users on the power 7 720 system all day long. We also run java application that validates our customer logons to our web servers.