Jazzer,
You mentioned the 'Scottish Gliding Centre', which is based at Portmoak. Formerly known as Scottish Gliding Union, it is the closest to Edinburgh and one of the larger clubs in Scotland. Depending on where you live, it may or may not be the most convenient for you.
The other clubs I know of in Scotland are -
Deeside Gliding Club at Aboyne,
Cairngorm Gliding Club at Feshiebridge,
Highland Gliding Club at Easterton and
Dumfries and District Gliding Club at Falgunzeon.
Just across the border there is also the Borders Gliding Club at Milfield.
All will have friendly as well as grumpy pilots...
Both SGC and Deeside Gliding Club operate during the week as well as at weekends form late Spring till late Autumn. The others are largely weekend operations except for occasional summer weeks.
SGC, Deeside and Cairngorm will probably all have visiting sailplanes hoping for high level wave flights just now - always fun to hear about.
Enjoy yourself, and India Four Two is absolutely right; you will never look at a sky in the same way again.!