If you're going for the famous hostels in May, most def. reserve. Actually, I would say it never hurts to reserve. At least you know you'll never be without a bed and if you reserved and didn't get a bed, than you can bitch about it and sue the hostel. Then you just gain more.
Brazil, Canada, Greece, Turkey, Mexico, England, Wales, Ireland, Scotland, Northern Ireland, Portugal, The Netherlands, USA
Belfast, Northern Ireland