In fact, ideological terrorism has an almost perfect record of failure from 19th century Anarchists to the Weather Underground and similar groups (on both the right and the left) in the 1970s. The most any of these movements achieved was to bring authoritarian governments to power or to force governments to curtail civil liberties.
For a nationalist movement, bombings and assassination can work because the victims are seen as being on the other side, and because the weapons are the only ones available. As long as Al Qaeda was attacking targets in Western (or at least non-Muslim) countries, they could draw on Arab/Muslim nationalism as well as Islamism for support. But attacks in Muslim countries are a different matter. Inevitably, the majority of victims will be ordinary people going about their business, and it is the terrorists who will appear as demonic outsiders.
As Lott notes, Al Qaeda propaganda is trying to neutralise this effect, for example by claiming that the victims of the Saudi attacks were CIA translators. But this sort of stuff only convinces people who want to believe. Lots of Muslims wanted to believe that Mossad was tangled up with the World Trade Centre attacks. Not many will be motivated to believe spurious justifications for attacks where they themselves could easily have been among the victims.
Looking at longer term strategic implications, the big impact will be on Turkey’s case for admission to the EU. Supporters will undoubtedly push harder – Jack Straw has already made this clear. While some of the opponents, who don’t want a Muslim country to join Christian Europe, will be hardened in their opposition, it’s going to be very difficult for opponents like the German Christian Democrats to articulate this kind of line without being viewed (correctly IMO) as capitulating to terrorism. Of course, there’s still the perennial problem of Cyprus, but I expect the Turkish government will finally see the need to dump Denktash and support reunification without quibbling too much over terms.