I use it a lot - you need to add some beeswax to keep it flexible - about half and half is a good starting point, melt the wax first and add the resin in small pieces. It was usual to add finely powdered material to this as a tempering agent - dry dung, grass fibres charcoal etc. For fixing metal into wood some recipies also included sulphur - this corrodes the metal a bit and the corrosion products expand fixing the metal in place.
the beeswax/pine mix also makes a great varnish if you dissolve it in hot turpentine.
Birch tar is wonderful stuff, you can replace the pine resin with birch tar if you boil the birch tar down until it starts to set, it forms a more flexible pitch and can be used without further additions.
To use them just reheat - you can store small blobs on the end of sticks to save having to reheat the whole lot.
Oh - just in case, these methods involve boiling flammable substances - best to do it outside in small batches with some means of fire control - wet towel or something - never chuck water on it ( especialy turpentine ).
Realgar