Time Series in OBIEE compared with Discoverer

I just finished reading through Mark Rittman's post titled OBI EE, Time Dimensions and Time-Series Calculations Here, Mark goes on a wee journey to look at how time-series queries in OBIEE (as the title suggests :)) can be set up. As can only be expected this is an interesting read.
His post comes at a good time for me, as we are well under way to setting up time-based querying for a client.
Currently we have a simple time dimension that is shared between several datamarts. Most dashboards and Answers reports will have some sort of Year-Ago comparison, so this will have to be done right from the get-go ...