No overheating issues at all. Leave it on standby when not in use no problems. Might be a different matter though if you are planning to installing a HD?
Build quality on the Dune HD Smarts are top notch. Ive had a WDTV, the optical out socket broke after 6 months use, the Dunes are a different beast to the WDTVs.
One thing I will say is make sure your amp/blu ray home cinema system has HDMi out if you want to watch media with Dolby True HD, DTS HD Master Audio. Optical out can't handle the bandwidth.