On the main web screen (we call it the Web Interface - WebIF) click "Package Management" and then "Update package list from Internet". When that completes, click the "Available" tab and the list summarises what's what. Notes about each package are available in the Wiki, and many of them have their own discussion topics in the forum. By going into "Settings" (WebIF) you can enable advanced packages (the development section) which are otherwise hidden.
For example, several of us view HDR-FOX recordings remotely using an HD-FOX as the streaming player, but instead of being limited to the DLNA capabilities we make the HDR a network share and mount it as a virtual USB drive on the HD using auto-mount on the HD and samba on the HDR. However, this would not work if the recordings remained encrypted on the HDR drive, so auto-unprotect plus unencrypt decrypts recordings in the background soon after they are made. This also makes them available for transfer anywhere else without being rendered unplayable, and if it became necessary to copy them off for transfer to a replacement HDR-FOX they would play (not the case if still encrypted). Universal decryption and network sharing also makes the content more accessible to a wider range of media players - eg Splash Lite is a good player on the PC able to handle HiDef, but lacks DLNA capability (and even if it did, the stock HDR-FOX would refuse to serve HiDef content to it).
Some of us don't like series recordings going into series folders, so flatten moves recordings into the top level soon after the recording is completed - except those we've marked as not for flattening in the WebIF. The destination folder for a scheduled recording can also be manipulated in the WebIF schedule viewer. Why? Because if you are just time shifting and want to view whatever has been recorded on a first-in-first-out basis, it is a pain having to trawl through a load of series folders to find what's next. Then there is undelete, which creates a recycle bin so that any recordings you delete from the WebIF or the handset OPT+ button get transferred there and then deleted a week later (adjustable) - meanwhile you can play them from there or rescue them if required. One ruse I have hit on is to record unimportant stuff straight to the [Deleted Items] folder, then it gets expired automatically!
There are packages which protect us from external manipulation: disable-ota prevents the box waking up every night to check for an automatic update (we'll decide what gets installed and when, thank you), and 1.02.27 has a nasty habit of forcing a retune whether you like it or not - so disable-dso sorts that out (retunes kill off the recording schedule, and it would be an automatic scan so may not give the appropriate results anyway - you don't want multiple transmitters because they play havoc with AR). On the subject of the recording schedule, the CF backs up the schedule daily, and you can initiate a manual backup, or restore any backup, from the WebIF.
This scratches the surface - the list goes on and I'm sure everyone has their own favourites!