Clustering issues

Hi Team,
I have few queries on Clustering concepts  and below are the queries,

1) What is the structual difference between sql server cluster 2005 and sql server cluster 2008?
2) Steps for upgradtion/patching on both active/active and active/passive cluster nodes?
3) What is the differnce between Clustering and Alwayson high availabily in sql server 2012?
4) Common issues in clustering and how to fix it?
5) Troubleshooting issues in clustering?

Thanks in Advance,
Sarvan.N