Hi Frank,
I do remember 'Reliability Rides' but never took much interest in them. How do they work?
Reliability rides are just something with a bit more organisation than a normal bike ride, with a set route and a target time range to aim for.
Sportives are pretty similar from the cycling point of view. What is different is the marketing and the atmosphere that they have managed to build up. They have been made more accessible than more traditional forms of competitive cycling (time trialling, road racing) or even audax so they have a high proportion of relatively new cyclists. While this is to be applauded (and has probably made as big a contribution as anything to the resurgence in popularity of cycling ), an inevitable downside is that a larger proportion of the riders than with other forms of organised cycling have not ridden with clubs and have not learned the best practices of how to ride in groups, so you hear stories of pile-ups and near-misses.
As the poster above mentions, they are generally professionally run by events companies rather than by amateur cycling clubs. Therefore they are generally quite slick. While they can be expensive to enter, they do give quite a bit of value. There is generally a signed route, free energy bars and drinks (but not proper food!) and good changing and showering facilities.
Personally they are not my cup of tea (I mainly do audax and time trialling) but I did one out of curiosity last year, was impressed, and think they are a good thing for cycling.