The lack of memory expansion on the Xperia S might be a problem (or frustration) to some, but there IS a way to add more memory if you're, say, wanting to watch a film on it (perhaps connected to your HD TV).
It's NOT likely to be particularly convenient when you're out and about, although it might be useful if you need to get data from another memory card (e.g. a digital camera) using a card reader - as long as it can be powered via the USB port. I could, for example, access photos from my DSLR and upload them to Dropbox via the phone without having to copy anything to the phone first.
I bought one here;
GENUINE NOKIA USB OTG CA-157 CABLE ADAPTER FOR N8 C6-01: Amazon.co.uk: Electronics
It cost me £1.79 with free postage and turned up in two days (it's sent by Amazon so if you ordered early in the day there's no reason why it wouldn't arrive the next day). You could barely buy half a pint of lager for £1.79!
I am only mentioning the above link as it is the one I personally got, there are plenty of other people selling them - some original Nokia ones, some Samsung and some copies. I went with Nokia as I had one with the N8 ages ago (and wish I'd not lost it). I have no affiliation, but can confirm that I got the cable I bought (some comments/reviews suggest they got the wrong thing but that wasn't the case for me).
I have connected a USB flash drive to the phone and it immediately detected it, and it now shows as another storage device. Alternatively, you could add a wireless dongle to attach a keyboard or mouse, or possibly even a USB keyboard or mouse directly. In other words, no need for a LiveDock. (Apologies to those who knew the LiveDock was just a stand with a USB on-the-go cable incorporated within it if that sounds patronising)
For the price, I'd recommend everyone with this phone (or any other Xperia model from 2011) gets the cable. In fact, it would have been good if Sony had considered making its own cable and including it in the box! The only downside is you can't charge the phone while you're using an accessory (hence the need for a LiveDock), unless someone knows of a cable that has a branch coming off to connect a PSU?