This is really a question of style -- not though in terms of one position is the sentence is always better or always worse, but as a matter of subtle effect in terms of emphasis and rhythm. All three of these are perfectly legitimate grammatically:
Today, I have lost some faith in Wikipedia.
I have lost, today, some faith in Wikipedia.
I have lost some faith in Wikipedia today.
Of these three, the first is the most formal. Generally speaking, it is true that formal English does tend to place temporal and other limiting information at the beginning of the sentence. Word order is a fussy thing for English grammarians precisely because English is not an inflected language. Adverbs, like today, however, have retained some freedom for themselves to move about.
The second example could be construed to be a 'commanding' use of the language. This is the voice of someone who is, undoubtedly, in control of where to place his or her interruptions. It has the effect of placing some additional emphasis on "lost."
The third example is the most conversational, but should in no way be construed as being incorrect on any level. It is perfectly legitimate.
But this is not to say that near is not the end of grammar! Sometimes I do wonder if the fate of the world is not a downfallen one and near at hand. But I'm sure that in the end, text messages will be revealed to have a grammar all their own. And in the future, perhaps even Linguists will use them. =)