Well clearly any sort of life that comes anywhere close to life as we know it could not possibly live on Venus! And certainly cities couldn't exist there. Basically that stuff all sounds just plain nuts! How exactly did he claim to acquire this "knowledge?" Don't they also claim the universe is hundreds of trillions of years old?

I'm sure you're aquainted with old saying, "The road to Hell was paved with good intentions?"

I'd recommend borrowing a copy of Dianetics from your local library. It pretty much epitomizes the above statement.

My own opinion after reading it was that Hubbard was genuinely quite concerned for the well-being of the world, as most people were during the time he wrote Dianetics, because of the very real threat posed by nuclear weaponry and international tensions. He invented his entire mythos as a sort of modern allegory, with a rich and entertaining backstory that would really reel people in, in order to illustrate the dangers of totalitarianism and grotesque stockpiling of weapons of mass destruction.

There's so much extremely compelling and sound metaphor in his works that I can't help but sympathesize with him here.

Unfortunately, that's not where it ended. Hubbard clearly felt that he needed to take radical action, and this is also spelled out in Dianetics. Dianetics is all about surrending yourself to the whims of scientology and mistrusting any and all other forms of diagnosis or influence. Hubbard clearly felt that psycho-analysis and psychoactive drugs could be used to undermine what greater goals he initially had for the 'church', so attacked them and demanded that followers of his doctrine isolate themselves from such things. This, of course, snowballed - and soon whatever better intentions Hubbard had were overtaken by legal scandal, his own greed and the organization's thirst for power as it grew. The later mythos became more vague and ominous, simply being used as a vehicle to attack other religious groups and persons that Scientology had to compete with, and I'm certain that Hubbard became more concerned with securing himself a throne of power than advocating for the disarmament of nuclear weaponry.

Still...

I think I'm going to change my sig to something a tad more meaningful now.

Seriously - do approach it with a skeptical eye, and perhaps prepare yourself to read some professional literature on psychoactive medication and psychology when you're done. The book is quite good at appealing to your emotions and twisting your perspective, and I'd think it dangerously naive of anyone to approach Scientology thinking, "Bah. They'd never suck me in."

There is also the litany of extraordinary claims regarding Hubbard himself.  The church of scientology states as biographical fact:

• Hubbard became the youngest Eagle Scout ever, at age 13 
  (The Boy Scouts do not officially keep track of such data, but boys as young as 10 have achieved the badge.)


• Hubbard became an honorary member of the Blackfeet Indians in Montana
    (There is no evidence of this, and the Blackfeet reservation was actually over 100 miles from Hubbard's home in Helena.)
     
• Hubbard studied extensively with spiritual men in the Far East
  (His time in the Far East amounts to brief stopovers in China en route to visiting family in Guam, and his diary entries from the purported time do not mention such studies.)


• Hubbard was a nuclear physicist, and even consulted by the government
  (His academic record shows he took one course in nuclear physics at George Washington U., which he flunked.)


• Hubbard suffered severe combat injuries in WWII, leaving him blind and lame.  While bedridden, he developed Scientology to restore himself -- including 20/20 vision
  (There are no military records indicating Hubbard saw any combat whatsoever.  Rather, the records that are available indicate he performed incompetently, even firing into Mexican waters.  Also, there are several photos of Hubbard wearing glasses, hardly a requisite with 20/20 vision.  In fact, Hubbard applied for and received Veteran's disability.  Which ironically renders false both his claim of suffering combat injuries and that Scientology can restore one to perfect health.)

Christians have the advantage that their beliefs are separated by 2 millennia, rendering disproof of their claims difficult if not impossible.  This of course does not relieve them of the original burden of proving their claims, but they need only argue against a lack of evidence; they do not have to contend additionally with actual evidence or eyewitness testimony running counter to their claims, as Scientologists or Mormons must.   

Nonetheless, we see the same confirmation bias in effect.  christians come up with all order of excuse for the lack of expected historical evidence for their beliefs, e.g., the evidence was destroyed by the Romans when putting down the revolt in the 1st century.  scientologists for their part claim that anyone who disputes Hubbard's/scientology's claims is a "religious bigot" and "hiding crimes".  A February, 2011 New Yorker article about director Paul Haggis' defection from scientology addresses in passing Hubbard's military record.  Their official excuse for the countermanding evidence is that Hubbard was involved in undercover operations with the government, so they made a duplicate version of his record out of security concerns.  The reason for such desperate excuse-making is clear.  This is how scientology spokesman Tommy Davis responds when asked about Hubbard's dubious claims (from the article):

This is reminiscent of the concession in 1 Corinthians 15 that christians are "the most to be pitied" if the resurrection is false.   The same way christians need the resurrection to be true, scientologists need Hubbard to be a war hero (and nuclear physicist, expert on Eastern spirituality, honorary Blackfeet Indian, youngest Eagle Scout, etc.).  

So whether it's science-fiction tinged psychotherapy or Bronze age zombie snuff, neither lack of evidence nor falsifying evidence will dissuade the true believer.