Well, it turns out that long-term exposure to the heat produced by the computers can cause something called "toasted skin syndrome."
Long-term, low-grade heat, like that from a laptop, can cause a mottled appearance and sometimes permanent darkening of the skin. Also, it can, in very rare cases, lead to skin cancer according to Swiss researchers from University Hospital Basel ("‘Toasted Skin Syndrome' Warning for Laptop Users," NewYork.CBSlocal.com, Oct. 4, 2010).
For a commonsense solution, experts recommend limiting direct contact between laptop and skin by using a heat shield. Best of all, place the laptop on a desk or stand.