A fascinating and unexpected outcome of the recent analyses of higher eukaryotic genomes has been the demonstration of pervasive transcription from non-protein-coding genomic sequences. Indeed, the preliminary results of the human ENCODE project indicate that whereas protein-coding sequences occupy less than 2% of the human genome, close to 93% of the genome is transcribed into RNA [1]. Although intronic sequences occupy a significant percentage of the non-protein-coding sequences in the genome, the majority of the independent non-protein-coding transcripts belong to the group of long non-coding RNAs (lncRNAs) - RNAs that are more than 200 nucleotides in length and do not appear to have any protein-coding potential [2-4]. A few members of this mysterious and highly understudied group of RNAs have been known for a long time, for example the Xist and Air RNAs; however, the majority of these transcripts have been only recently discovered in high-throughput transcriptome analyses. Furthermore, most of them are expressed at low levels and many do not show a high level of sequence conservation. Thus, the functional significance of this class of RNAs as a whole is still very poorly understood and subject to debate and speculation.