Being a Red Dwarf fan since I was 7, 'Smeg' has always been part of my family-friendly profanity database. I use it when there are small children / elderly ladies with heart conditions around because I couldn't care less about kids hearing profanity but I can't be doing with aggro off parents.
I find words like "frak" and "frell" to be somewhat lame and "Gorram" doesn't sound right unless grunted by Adam "Jayne" Baldwin.
I can't say I have had call to use it yet but I was playing Mass Effect 2 for the first time the other day and I got a good laugh out of the term "daddy-bags" (bollocks) and will add that to my lexicon for future use!
And yes, "Custard" was mentioned in one of Jeremy Clarkson's Sunday Times' columns. Trust me - I have all the books!
Wardy