Big Data: Who use Hadoop

http://wiki.apache.org/hadoop/PoweredBy

And here is information from Manning Hadoop in Practice ebook:

Hadoop has a high level of penetration in high-tech companies, and is starting to make inroads across a broad range of sectors, including the enterprise (Booz Allen Hamilton, J.P. Morgan), government (NSA), and health care.

Facebook uses Hadoop, Hive, and HBase for data warehousing and real-time application serving.8 Their data warehousing clusters are petabytes in size with thousands of nodes, and they use separate HBase-driven, real-time clusters for messaging and real-time analytics.


Twitter uses Hadoop, Pig, and HBase for data analysis, visualization, social graph
analysis, and machine learning. Twitter LZO-compresses all of its data, and uses Protocol
Buffers for serialization purposes, all of which are geared to optimizing the use of
its storage and computing resources.

Yahoo! uses Hadoop for data analytics, machine learning, search ranking, email
antispam, ad optimization, ETL,9 and more. Combined, it has over 40,000 servers running
Hadoop with 170 PB of storage.

eBay, Samsung, Rackspace, J.P. Morgan, Groupon, LinkedIn, AOL, Last.fm, and
StumbleUpon are some of the other organizations that are also heavily invested in
Hadoop. Microsoft is also starting to work with Hortonworks to ensure that Hadoop
works on its platform.

Google, in its MapReduce paper, indicated that it used its version of MapReduce
to create its web index from crawl data.10 Google also highlights applications of
MapReduce to include activities such as a distributed grep, URL access frequency
(from log data), and a term-vector algorithm, which determines popular keywords
for a host.

The organizations that use Hadoop grow by the day, and if you work at a Fortune 500
company you almost certainly use a Hadoop cluster in some capacity. It’s clear that as
Hadoop continues to mature, its adoption will continue to grow.

As with all technologies, a key part to being able to work effectively with Hadoop is
to understand its shortcomings and design and architect your solutions to mitigate
these as much as possible