Muqtada al-Sadr, occulted head of Iraq's Jaysh al-Mahdi for almost two years, resurfaced yesterday in Turkey--where he was received by both Prime Minister Erdogan and President Gul.  According to al-Jazeera (http://english.aljazeera.net/news/europe/2009/05/20095115592374529.html), "Turkey's Anatolia news agency cited unnamed diplomatic sources as saying that al-Sadr's visit was aimed at 'holding consultations on the political process in Iraq.'" But wouldn't such consultations better be held with the actual elected leader of Iraq, al-Maliki? And indeed, Gul traveled to Iraq and met with the Iraqi PM earlier this year.  Why would the Turkish leadership host, in effect, an Iraqi opposition leader?  It would be as if Canada hosted, say, Newt Gingrich or Rush Limbaugh for a series of meetings (and didn't arrest them for violating their "hate-speech" laws). 
Speculations:
1) This is part of Turkey's AKP, Islamist-lite leadership's effort to play regional power broker, and is motivated solely, or mostly, by geopolitical concerns such as Turkey wishing to put a little pressure on the Baghdad government because of frustrations over the growing power of Kurds in northern Iraq.
2) Erdogan, Gul & Co. in the AKP are placating Iran by hosting their main Iraqi representative; remember, al-Sadr just spent his occultation ("hiding"--a term in Arabic reserved for the state of the 12th Imam, the Mahdi, for the last millennium or so) in Iran, allegedly studying to attain the rank of ayatollah. 
3) Iran is using al-Sadr as a da`i, a "missionary," bringing their chiliastic call to join the legions of the soon-to-arrive Mahdi to the Turks; Khamaenei and Ahmadinejad may reckon that the moderately-Islamist leadership of Turkey might be receptive to this Mahdist da`wah. 
 4) The Turkish leadership harbors neo-Ottoman, irredentist claims itself on the region and keeping Iraq hobbled by a powerful opposition group in its south is one way to ensure the country never totally coalesces around Baghdad's control...and the Americans won't be there forever.
If anyone has other ideas--or cares to comment on these--feel free to contact me: tfurnish@bellsouth.net