Keep Circulating the Tapes: The show has never been fully released on DVD; only a few scattered "best of" compilations, most of which are only in Europe.
And while it's no substitute for a physical release, the first season is available in the Canadian and US iTunes stores.
Series 1and 2 have been available in the UK for quite some time now. Prior to this, only the first six episodes of season 2 and the first two episodes of season 1 were available on VHS, along with the four specials, which remain unaccounted for on DVD.
According to The Other Wiki, the whole series, including specials, has been released on DVD in Germany... with only a German audio track.
The Other Darrin: A few characters were recast during the course of the series and specials. In particular Melissa had four different voice actresses.
Talking to Himself: Len Carlson voiced Bert and two of the pigs, as well as numerous ancillary and minor characters. In "The Phantom of Sneer Mansion!" and (arguably) "Black Belt Bentley!", Bert's voice is mistaken for another voice performed by Carlson. Other cast members also voiced multiple characters.