What I want to know is, based on actual encounters, what has happened to people that makes them think it is not practical, or has anyone had a failure of their Aikido?
You are assuming actual encounters. The recent posts appear to have been started by individuals who are either inexperienced, or engaged in a "my MA can beat your MA...Oh yeah?" argument with some local rummy whose mastery of aikido may (or may not) have included its proper pronunciation.
Was it Jun who quoted Ikeda Sensei?: "Its not that aikido doesn't work, YOUR aikido doesn't work". Think about this. If we as a group of aikido students were in doubt of aikido's efficacy, why would we spend so much time and effort doing it? IMO, the quote from Ikeda is a clear, concise and final answer to all those impatient, non-practitioners who enter the website, beat their chests and proclaim the martial superiority of their style/view. Let'em whine and rant. I've got some training to get back to....