I found this the most helpful (though, it's a year old) - http://yahoohadoop.tumblr.com/post/98256601751/pig-and-hive-at-yahoo
It specifically talks about Pig vs Hive and when and where they are employed at Yahoo. I found this very insightful. Some interesting notes:
On incremental changes/updates to data sets:
Instead, joining against the new incremental data and using the
results together with the results from the previous full join is the
correct approach. This will take only a few minutes. Standard database
operations can be implemented in this incremental way in Pig Latin,
making Pig a good tool for this use case.
On using other tools via streaming:
Pig integration with streaming also makes it easy for researchers to
take a Perl or Python script they have already debugged on a small
data set and run it against a huge data set.
On using Hive for data warehousing:
In both cases, the relational model and SQL are the best fit. Indeed,
data warehousing has been one of the core use cases for SQL through
much of its history. It has the right constructs to support the types
of queries and tools that analysts want to use. And it is already in
use by both the tools and users in the field.
The Hadoop subproject Hive provides a SQL interface and relational
model for Hadoop. The Hive team has begun work to integrate with BI
tools via interfaces such as ODBC.