Siri may seem like a gimmick, but we can see its value in certain situations such as when it's used hands-free while driving or if you have a visual impairment. At the moment, Siri only recognises British, American and Australian English (although it struggled with some thick regional accents), as well as French or German, with more languages promised. If you feel conspicuous speaking to your phone, Siri works when holding the iPhone 4S to your ear as if you were making a phone call or when used with a hands-free set.
Although technically separate from Siri, the system-wide voice dictation feature in iOS 5 almost certainly uses the same server back-end and processing algorithms as Siri. A microphone button next to the spacebar on the keyboard allows you to dictate text instead of typing it. Like Android's voice dictation system, text is more accurate if you speak clearly and avoid using colloquialisms and contractions, but it usually recognises punctuation.
Whether we'll still be using Siri a year from now depends on how quickly Apple can improve the server-backend and the algorithms for this beta-labelled feature. For example, some features available in the US, such as traffic data and local business recommendations, are currently unavailable in the UK, but are supposed to arrive sometime in 2012. There are plenty of other features in iOS 5, but apart from Siri most are shared with older iPhones, so they're covered in our separate, upcoming iOS 5 review.
