How does System Information break down the Storage report? When I access the Storage report via About this Mac > More info... I am noticing some strangeness: I see quite significant amounts being reported for file types that I don't have a lot of on my hard disk i.e. 1.26 GB Audio; 9.94 GB Movies; 4.72 GB Photos...

Using Disk Inventory X I noted that the most significant consumers of my disk space at the moment are the backup of my iPad (which is categorized as iTunes Document by that app and mostly consist of iOS apps and a couple of books) and my DropBox folder (which has some pictures and movies but not that much given I only have under 12 GB of DropBox space).

How does the Finder categorize file types and indeed what is 'Other' which is currently consuming 29.44 GB of disk place?

cheers
Other is a catch-all by taking the drive's max capacity and subtracting the sum of all other counted file sizes. So, if your drive has corruption where many blocks are unavailable or lost, you will see large other "allocations". 

If the other space remains the same after running disk utility to verify and/or repair the volume then you can assume it's really files taking that space.

The categorization comes from spotlight indexing, so you could search here how to rebuild that index if you suspect bad metadata leading to an incorrect storage report. 

The simplest way to rebuild the metadata (spotlight) index is to simply add your hard drive to the spotlight privacy list in system preferences and subsequently remove it. The built-in help should have a guide if you're not sure how to refresh all spotlight data.