1) where can i find articles from Estonia conference? There were several conferences in Estonia including TFP, ICFP and Haskell Workshop. Go to http://www.cs.ioc.ee/tfp-icfp-gpce05/, look at the program, type in the title of the talk and most of the time google will give you a copy of the paper.
2) they all say that GADT is great, but i personally don't "feel" GADTs. can anyone write a paper about it for beginners like me, or may be just collect examples of using GADT in real programs? They were not all about GADT's, but there were a few about them. The talk on Yampa was probably the most introductory and accessible GADT talk I saw. (http://portal.acm.org/citation.cfm?id=1086365.1086374 , http://www.cs.nott.ac.uk/~nhn/Publications/icfp2005.pdf)
Thanks Neil