Sounds to me like Qatar (like EK and the other big airline in the region that CANNOT ever be named again), will work their pilots very hard - right up to the legal limits. If you are employed by these airlines, expect to work pretty hard - just expect that going in and you likely won't be too surprised.
At Qatar, the A320 fleet seems to be a workhorse with both day and night flying. That said, others on these forums claim that the 777 fleet is even more challenging for FOs (to this day I have still not seen an actual 777 roster to contradict that). Someone said the A330 fleet is also busy - not sure about the A300-600R freighter fleet. So, from what I have heard and read, just expect work hard regardless of which fleet - go in with your
eyes wide open 
and you will not be so surprised.
Personally, if I had the relevant/competitive experience, I'd hope for a 787 FO slot later this year or in 2013 as the fleet ramps up - but that's only me (not speaking for the jaded pilots on this forum who could
not care less about fleet). From what I have heard in various announcements, that fleet (with 60 orders and options) should do some interesting mix of longhaul (several North American and European routes announced - including LHR) and shorthaul - probably Gulf and India night turns... That would be great for me since I have not seen much of the world from my cold/dark/wet/dank corner of Europe. No doubt the work will be exhausting on the 787 fleet as well as QR management will find a way to maximise productivity for all.
Perhaps the A320 fleet rosters have changed or improved since the post below was written a few months back... Regardless, the following QR A320 roster found in this forum was quite
enlightening :
For those contemplating joining QR, here is an actual roster for A320 Captain.The month and specific destinations have been omitted to protect the innocent. All times are based on DOHA which is where your body clock will be.
Day 1. day off at out station in Europe.
Day 2. wake-up-call 2150 to fly back to Doha.
Day 3. Land DOH 0535, report again 2245 for Gulf turn-around (3h on gnd).
Day 4. Land DOH 0645, report again 0000 for Gulf turn-around (3h on gnd).
Day 5. Land DOH 0555, report again 1945 for Gulf turn-around ARR DOH 0000.
Day 6. report 1800 regional turn-around
Day 7. Land DOH 0015, report again 1345 for three-sectors (Gulf + layover),
Day 8. land at outstation 0120 (layover), wake-up-call 1500, land DOH 2230
Day 9. off
Day 10. off
Day 11. report 0650, four-sectors around the Gulf, land DOH 1700.
Day 12. report 2245 for Gulf turn-around (3h on gnd)
Day 13. land DOH 0645, report again 2345, two sectors for layover.
Day 14. land at outstation 0830 (layover)
Day 15. wake-up-call 0855, two sectors, land DOH 1910
Day 16. off
Day 17. report 2345, regional turn-around
Day 18. land DOH 0545, report again 1925, one sector for layover
Day 19. land at outstation 0055 (layover), wake-up-call 2300
Day 20. operate back to DOH followed by a Gulf turn-around, land DOH 1050
Day 21. off
Day 22. off
Day 23. ground school (ex. crm, security, dangerous goods)
Day 24. report 1045 Gulf turn-around plus regional turn-around, land DOH 2230.
Day 25. off
Day 26. off
Day 27. report 0700 one sector to Europe for 22h layover.
Day 28. wake-up-call 1030 fly to DOH plus Gulf turn-around, land DOH 2320.
Day 29. report 1230 one sector to Europe for 24h layover.
Day 30. wake-up-call 2200 to fly to Doha
Day 31. land DOH 0530.
This roster has the minimum eight days off, of which seven are at home and one is in a hotel (Day 1). 92 block hours and 160 duty hours (= salary QAR42,500). Generally it is unusual to get days off at outstation.
You will often get a 10-12 day pattern with a combination of day and night flying with the one legal day off in the middle. Rest of the month will obviously be better.
QR operates strictly according to legality. No regard is taken for family issues, fatigue-issues or the flight safety implications fatigue has. You will be tired beyond your imagination, but you will get a decent meal at 3am if you wish.
By the way, management cancelled one week’s leave for all A320 pilots this winter.