I have not noticed the smell on my iBook, but a possible source is that the plastic is cooking. The constant heat from having the iBook on could be causing a breakdown of the chemical structure of the plastic. Until I smell the smell, I could not pin point the source within the iBook. Usually softer (more plyable) plastics are effected sooner. The heat is not high enough to show scorching, but it could be cooking anyway. Concerning Safety, the problem is not critical, i.e. the iBook will not ignite as some computers did when lithium batteries were first put to use. Also, it is possible that the smell will go away. When the SO2 (rotten egg) is driven off the smell should subside, however, the resulting chemical structure of the plastic may be different.