Well, I am a pilot and can give you first hand info, based on UK.
1.What kind of flying you do,i.e. shorthaul/ longhaul and what is your typical weekly/ monthly routine?
Shorthaul will generally involve either 2 sector days with the charters or multi sector days with the low costs, getting back to base most nights. With BA you get more "tours" - ending up in different haunts in Europe and UK for a few nights.
Longhaul obviously entails longer sectors, so you would do one sector and then go to a hotel. Minimum rest is 12 hours or the length of previous duty; some charters do operate on near to minimum rest at certain destinations but other stopovers will be a few days.
2.How often do you have to work at weekends?
With most airlines you will always do some weekend working, as that is the busiest part of the week. I think only in BA can you choose to work less weekends as you gain seniority.
3.How much time do you have to spend away from your families, say over a month period? Can this cause problems?
Depends on the airline/ type of flying. As I mentioned, charter airlines (ie. the holiday airlines) and low cost generally get back to base, whereas with BA and long haul flying you'll be away much more. You mgith do 4 or 5 long haul trips in a month. With short haul you'll probably get 8-12 days off a month, and some home standbys. However, some of the flights will be night flights, with days off afterwards. Your days off are meant to be used for recovery and resting before your next duty period starts again.
4.How much spare time do you have in comparison say with someone who works a regular 9-5, Mon-Fri job?
Depends on the airline. I have gone through periods of working 7 days on-2 off although now it tends to be much better, perhaps 5 or 6 on-2 off. In the summer you'll generally be flying 5 or 6 days a week, but there is a maximum number of duty hours in the week - 55 - and you can't fly more than 100 hours in 28 days (although obviously your duty time is greater than your flying time). In the winter it is sometimes quieter (depending on airline) and you may find that you are flying only 3 days a week with lots of standbys. Standbys are good as you can do what you like providing you are within a certain callout time, usually 1.5-2 hours. So in the summer, unlikely to see much of your friends, unless they are around on a Tuesday and you can't drink anyway unless you drink the first night before your day off and then you are too knackered anyway!!!
5. Is it a sociable job, do pilots socialise/ go out drinking much with each other?
I think pilots and crew are generally sociable, on a nightstop they generally go out, but outside of work I haven't found there is a huge amount of socialising, except with maybe one or two colleagues.