SQL Analysis Services - SSAS
The most significant balancing act to consider is whether your need for real-time reporting outweighs the performance hit that both your OLAP and OLTP systems will take from using your OLTP data source directly as fact and dimension tables, and then bouncing ROLAP/HOLAP queries off of them. If the tables are all quite small, and the server isn't under heavy load already, then the penalty is probably negligible. If SSAS queries are going to kick off 500MB+ reads, then that's a problem.

And unless you're doing some kind of high-frequency trading, you probably don't need to have your SSAS database that up to date. It seems like SSAS is more useful for big-picture kind of summaries, and if the past few hours of data aren't included yet, it's not going to make a big difference to those running the reports (ask around to be sure, obviously).

We load our data warehouses and process the cubes each night, and that's typically plenty. We also have a few simple reports built against OLTP tables for viewing more targeted, up-to-the-minute data (stuff that's really more OLTP than OLAP in nature).