a good sign but probably won't mean much. The main IRA group has observed a cease-fire for quite some time, it's splinter factions that have carried out all recent acts of terrorism, and I doubt they'll observe this.
Ah but the point of this isn't whether they'll stop blowing people up or not... the point of this is political; the IRA having weapons and carrying out paramilitary/criminal activities was the big thing holding back the political process and the reason why NI is currently under direct rule.
With this out of the way, things are finally back on track and we could be seeing SF ministers in a Paisley led government pretty soon.