I just spent half a year in Jakarta. May not may be qualified to say much, but here are my initial reactions to the news:
1. The connection to the Manchester visit is important. The city has been anticipating this visit for months. Manchester United figures are ubiquitous in billboard ads. Beyond the immediate deaths, this is a shot in the face of popular culture.
2. Indonesia just finished their electoral cycle. Even the moderate Islamists (those not inclined towards violence) failed to make much headway in the legislative contest. People like the bland but relatively competent governance of the incumbent president SBY. Violent Islamists conducting a bombing campaign so soon after an election campaign suggests a ‘bombs over ballots’ argument has quickly won out in at least some extremist circles. One attack does not make a trend, but it is something to consider.

Hopefully they find the guys behind this quickly and introduce them to a firing squad.