Question: How many genes are imprinted in the human genome?

Context:
Among approximately 70 known imprinted genes are some causing disorders affecting growth, metabolism and cancer predisposition. 
By applying dsPIG to the mRNA-Seq data, we predicted 94 imprinted genes in 20 cerebellum samples and 57 imprinted genes in 9 diverse tissue samples with expected low false discovery rates. 
Interestingly, we found that, among biallelically expressed genes, at least 18 genes expressed significantly more transcripts from one allele than the other among different individuals and tissues.
To date, however, fewer than 100 imprinted genes have been identified in the human genome.
Approximately 150 imprinted genes are known to date, in humans and mice but, though computational searches have tried to extract intrinsic characteristics of these genes to identify new ones, the existing list is probably far from being comprehensive.
 In this study we analyzed the imprinting of 22 genes in human, mouse, and cattle and found that in only 11 was imprinting conserved across the three species.
However, 62 unique clones in the library were characterized, all of which were methylated and GC-rich, with a GC content>50%. Of these, 43 clones also showed a CpG(obs)/CpG(exp)>0.6, of which 30 were studied in detail. These unique methylated CpG islands mapped to 23 chromosomal regions, and 12 were differentially methylated regions in uniparental tissues of germline origin, i.e., hydatidiform moles (paternal origin) and complete ovarian teratomas (maternal origin), even though many apparently were methylated in somatic tissues.
Our findings suggest that there are at most several hundred genes in the human genome that are universally imprinted.
To date, however, fewer than 100 imprinted genes have been identified in the human genome.
The Imprinted Gene Catalogue now has more than 200 genes listed, and estimates based on mouse models suggest many more may exist in humans. 
Our findings suggest that there are at most several hundred genes in the human genome that are universally imprinted. With samples of mRNA from appropriate tissues and a collection of informative cSNPs, a genome-wide search using this methodology could expand the list of genes that undergo genomic imprinting in a tissue- or temporal-specific manner.
We confirmed that PEG10 is paternally expressed, identified one gene (ZNF331) with multiple lines of data indicating it is imprinted, and predicted several additional imprinting candidate genes. Our findings suggest that there are at most several hundred genes in the human genome that are universally imprinted.
Our findings suggest that there are at most several hundred genes in the human genome that are universally imprinted.

Answer: Among approximately 70 known imprinted genes are some causing disorders affecting growth, metabolism and cancer predisposition. 
Approximately 150 imprinted genes are known to date, in humans and mice but, though computational searches have tried to extract intrinsic characteristics of these genes to identify new ones, the existing list is probably far from being comprehensive. To date, fewer than 100 imprinted genes have been identified in the human genome.
Exact answer:  fewer than 100