As you may know, I am a big 3rd party tools advocate and have spoken about at conferences and SharePoint Saturdays. If you need seomthing that is not native to SharePOint or is just to hard and time consulimg to create, thjere is some tortued genius out there who has built the perfect solution. One such area is rollups. I always struggle to get rollups looking the way I want. I know SharePoint 2013 adds some slick new rollup features, but bottom line is I want it to be a fast, totally customizable solution that my clients can understand and can tweak as they see fit. I have become a huge fan of LightningTools Conductor rollup web parts for 2010 and 2013. In about 15 minutes I can create any rollup I want- across site collections, with filters, groupings, sorting conditional formatting, etc. all built in. I love this tool!
If you want to learn more, go to their web site at http://lightningtools.com/lightning-conductor-web-part-2013/ . There are also some