Interesting question. I researched this a bit now and the phenomenon is termed "numt" for  "nuclear mitochondrial DNA". This term descrives the transfer of cytoplasmic mitochondrial DNA sequences into the separate nuclear genome of a eukaryotic organism. It seems that most of these sequences are inactive. This [list][1] at pseudogene.net has a large number of sequences in a lot of different organisms, for humans insertion between 0,2 and 14,2 kb are listed.
For more information you can go to the list of papers I list below, this should be a good starting point:

 - [http://www.ncbi.nlm.nih.gov/pubmed/21151557][2]  
 - [http://www.ncbi.nlm.nih.gov/pubmed/11369110][3]
 - [http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0020273][4]
 - [http://www.ncbi.nlm.nih.gov/pubmed/15014143][5]
 - [http://www.ncbi.nlm.nih.gov/pubmed/18721785][6]

The papers should all be accessible, if not, let me know.


  [1]: http://www.pseudogene.net/
  [2]: http://www.ncbi.nlm.nih.gov/pubmed/21151557
  [3]: http://www.ncbi.nlm.nih.gov/pubmed/11369110
  [4]: http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0020273
  [5]: http://www.ncbi.nlm.nih.gov/pubmed/15014143
  [6]: http://www.ncbi.nlm.nih.gov/pubmed/18721785