Three weeks ago the weather was very warm here, and I hadn't yet re-arranged my PC case for the 109. I burned 16 discs in a row and they got very, very warm.
I scanned these discs just after the burn and they were not great but OK.
This thread rang a bell, so I re-scanned some of these discs yesterday, and to my dismay I discovered these discs have badly deteriorated! Ouch!
Same discs from the same batch burned at other times, and that didn't get hot, give perfectly normal scans (and btw scanned better to start with..). Discs involved were Traxdatas G04 and Verbatims MCC 02RG20, the latter being somewhat less affected (not a surprise to me).
My conclusion: unless one gives plenty of room to the 109 so to avoid overheating, there is a risk that discs won't have a normal lifespan...