Siri works in eight languages with 19 regionalisations (ie, English with Australian, UK, Canadian and US accents, Spanish for Mexico, Spain and the US, and Chinese divided into Hong Kong Cantonese, mainland Mandarin and Taiwanese Mandarin).
For those with accessibility needs, Siri now controls more elements of the system - for example, while boarding a flight with your hands full you can now invoke Siri and say 'Turn on Airplane Mode'. This is partly because Voice Control is gone, with Siri taking over its functions in addition to the services it already provided.
There's lots more about the new Siri abilities on TUAW.
My personal favourite tip for Siri is that you can set your title for when it refers to you directly. Therefore, Siri announces things like 'Sorry, Sublime Being Three, I can't look for restaurants in New Zealand' ... which also points out one of its localisation limitations.
To do this, just activate Siri by holding down the home button and wait for the beep. Now say 'Call me (favourite epithet here)'. This can be your name or anything else.
Siri will reply 'From now on, I'll call you (your preferred epithet). OK?'
You need to confirm, so just reply 'OK'. Fun! I have also added titles for other people, so I tell Siri "Call My Great Dad".
iMore has more on Siri customisations, for example adding phonetisised spellings so it says names more correctly.
Generally speaking, apart from the excellent new Control Center (sic) that appears when you swipe upwards from the bottom of the screen, giving you instant access to settings you access often including a flashlight.
There's quite a lot about Control Center on TUAW.
Folders now have greater capacity. Up to iOS 6, you could place 16 apps in a folder. OS 7 lets you have nine apps per page, and 14 pages per folder for 126 apps total.
A little blue dot next to an app name means an app has never been opened, as a handy reminder you have yet to try an app you have downloaded.
Some changes take a bit more of a mind-shift. In iOS 6, to switch apps you double-tapped the home button to access a list of recently-running apps, which appeared as a horizontal list along the bottom of the display. iOS 7 provides a tableau of screen shots enabling you to select an app with a single tap.
AirDrop finally makes swapping files between devices easier. It's available from Control Center. It can only swap files between people on you contacts list, but you can quickly change it to Everyone by tapping on AirDrop in Control Center for those work meetings - as long as they all do that as well. Then activated files (Notes, Contacts can send a business card to other users, Voice Memos, Photos which AirDrop lets you preview before accepting), Safari, Passbook, Maps and Podcasts, so far, and developers will hopefully add the capablities into their apps, too can be fired at anyone else on the same wireless network, once the Accept the transmission. Once the new Mac OS comes out, Macs will be able to send and receive to iDevices and vice versa the same way, saving lots of clunky workarounds we've been employing up till now.
Now, I can hardly wait for Mavericks (Mac OS 10.9).
[There is plenty more about Apple's new and free iDevice Operating System online, and I link to many handy sites on my www.mac-nz.com site under iDevice.]