I was out of the country for 11 months working in France/Portugal. It probably delayed my application a bit but other than that no problems.
From what I remember of what my AFCO told me if you're abroad for up to 6 months - no problem, 6 - 12 months they have to apply for a residency waiver, more than 12 months - look for another job. Obviously the country your visiting/working in/whatever will have some bearing on this.
The usual disclaimer applies: I could be talking a load of old arse - best bet is to check with your AFCO.