I'd like to positively mention Jean Quatremer (with whom I've been having a little dispute in the past about value of linking and blogosphere interaction) for his reactiveness.
In a blog post from Monday he informed readers that only some one hundred MEPs had shown up for the opening session of the plenary week of the European Parliament. On Tuesday, I read at @mvandenbroeke from the EP press unit that 408 MEPs had made it to Strasbourg.
I then wrote a little tweet mentioning the discrepancy to which Jean reacted quickly on Twitter explaining that his figure was from the opening of the session, the 408 was only reached at midnight.
Soon afterwards, he also updated his blog post mentioning both figures, (rightfully) adding that this doesn't undermine his argumentation regarding the ridiculousness of having a plenary meeting in Strasbourg under these conditions.
Update: The latest figure is 444 for Tuesday.