Nathan Jamin posted an interesting article recently on "How do you know you're agile" and I posted this comment:

There is definitely a spirit about being agile - a sense about it - a feeling as you suggest.

But I would say there probably are answers to the questions you pose - and in true agile form - there may be many answers depending who you are and what you want from agile – but fundamentally I think there is one that cannot be disputed and must apply to all agile cases - it should be possible to measure agility and it should be a process of continual improvement against an ever changing backdrop.

Being agile is ultimately about brining benefits to the business - delivering more value in less time and making more money with less waste. Without that no commercial enterprise is going to entertain it. I’ve seen teams who thought they were agile but were not realising the benefits and in fact were suffering because they were not taking the time to measure whether or not it was a success. From day 1 – why do you decide to become agile – because it will bring benefits – how will you know these have been realised – you will need to measure them – which should be straight forward assuming its some measurement you’re not happy with that made you decide to become agile to fix it in the first place.

So if you've introduced an agile practice and you want to know if that makes you agile - take a look at the KPIs - are they going in the right direction? Yes? Then I’d say you're agile!