Michael Segel, Solutions Architect at Nokia, had this to say:
Its big. :-)
Ok seriously... relatively speaking, the potential is unlimited.
Even though you have a finite number of companies, the permutations and multiple projects that would fit in to this 'big data' space make the opportunity huge.
Focusing on Hadoop, you have HDFS for storage, Map/Reduce for parallel processing, HBase/Hive for persistence, and then other components in the ecosystem like Oozie for control, Flume, Scribe for data acquisition... All of this components allow a company to look at their information in a different light. You can Use HDFS for storage, Add in HBase and not use map/reduce. You can use Map/Reduce on small data sets that are computational intensive, so you don't need HBase/Hive.
Think of Hadoop as being a new tool kit that lets you do things you couldn't do before.
This is why its a disruptive technology.
The reason you are seeing a huge growth in Hadoop and derivative technology is that its currently transitioning from leading edge to mainstream. Enough early adopters have shown success that mainstream fortune 1000 companies are starting to look at it.
Add to this start-ups and SMB where the low cost and shortened runways make adoption of Hadoop easier.
Your limitations are human ones. Potential adopters vision and budget are your only real constraints.
I think it summarizes this so well that I could not resist re-posting.