The issue here is not numbers, and I address this to the muslims in particular.
If u've studied the early Muslim battles in the History Of Islam, Victory was never in the form of 'who had the gretest amount of followers', if this was the case, Islam would have never succeeded and spread to begin with.
The Battle of Badr for example:
At this battle the pagan army consisted of 950 fighters and the Muslim army consisted of 314 (including the Messenger S.A.W.). The Muslims were victorious in this battle, numbers was not an issue.
Forcing the pagans to bring reinforcements after 1 year where they approached the Muslim army with 3000 fighters compared to the 950 fighters at the battle of badr. (Before the battle of Badr, the pagans belittled the Muslims army, until they were defeated which was beyond their belief).
My point:
Whether Islam is the fastest growing religion or not, is not the full issue here, the issue is "what is each individual doing" (each individual being each person who contributes to the numbers shown in statistics), and this is somewhat (indirectly)addressed in the article posted, although to an extent it somehow reflects that All muslims are stronger in their faith than ever, this isnt the case (for 'All'), some people are still the same as they were before the 9/11 attacks or even the London bombings. In fact, I know a muslim who doesnt know what 'Al fatiha' is (the verse that every single Muslim needs to know in order to fulfil one of the most important pillars of Islam i.e prayer (5 times a day)) Notice I said"Doesnt know what Al-fatiha is", not "doesnt know Al fatiha". I asked this 'Muslim' whether they knew what Al-fatiha was, their reply: "huh! What's that".
What we should be asking ourselves is "Are All those who were born into Muslim families, following the correct teachings of Islam, if at all?" I can walk into centro bankstown today (or tomorrow i should say, the shopping centre is closed now) and give a staright forward answer: "No".
A number (or individual person) does not always equate to Action being taken. as mentioned previously in this thread by Sly fly (in different words). Actions speak louder than words.
I believe and know that most Muslims are good, and do follow their faith with full hearts directed towards the Almighty, and in fact, u'd even find that a large number of Muslim converts know more about Islam than those who've been living as Muslims their whole lives, I say this from personal encounter as well as through reading upon muslim converts and the enormous amount of time they devote to preaching the message of Islam. In fact ud find that most converts (or reverts) are in fact those who are very active in regards to Dawah (calling people to Islam).
If one organ of ur body aches, ur whole body aches and is affected. If this becomes the case (i.e when one Muslim is suffering, the whole muslim Ummah feels this persons suffering), No matter how great or how small Muslims are in number, they will always be successful if they live by this important part of Islam, which is how Islam was at the time of the prophet Mohammad (peace be upon him).