What is SOA!?
Here is an interesting article about SOA, short and clear.
Eight Things that Most People Misunderstand About SOAs by David Linthicum
Although, IMHO... he also maybe put some additional frustration on that SOA topic.
If you are new to SOA, or want to know more... check this two books:
SOA Principles of Service Design from Thomas Erl
SOA: Concepts, Technology, and Design from Thomas Erl