Google Earth 6 is the most current version of Google Earth.
As for the satellite imagery and layers hosted by Google, the same data appears on Google Earth 5 and Google Earth 6 alike. In fact, Google Maps for the most part shows the same satellite imagery as that in Google Earth but sometimes the imagery updates for one is slightly ahead of the other.
The frequency of imagery updates is answered in a related question. See related questions for details.
Soon after v5 ___________ Google Earth v6, as of March 24 2011, is out now. It is easily downloadable off of the Google Earth homepage.
No. The current best estimate is about 4.6 billion years.
Here is one of Google's announcements of ending Street View support for Google Earth versions 5.x and older. "With the most recent update to Google Earth (6.2), we are also finalizing our transition to a new method of delivering Street View imagery in Google Earth. This means, that the older versions of Google Earth (anything before 6.0) will no longer be able to access Street View. We held off making this change until now, when the vast majority of Google Earth users are on 6.0 (or later)." -- Google Jan 2012. Basically, Google decided to improve the Street View interfaces which would be implemented in the current versions of Google Earth for desktop and mobile platforms rather than keep supporting the older (less efficient) method of accessing Street View.
By taking the google spaceship from google mars. Kidding aside, you can either visit the google earth web page to download & install Google Earth desktop client or simply install the web browser plugin.
I got 947 miles from Google earth 6
Google gets its imagery from a variety of sources such as commercial satellite providers such as DigitalGlobe and GeoEye as well as from government and local agencies. Once the imagery is acquired by Google, it next has to be processed into the format and coordinate system of Google Earth's databases. Then it goes through a quality control process and processing system before getting distributed to the Google Earth database servers. This is one reason you usually do not find any imagery newer than about 6 months in Google Earth.
Yes, you can download Google Earth for free. There is also a professional version of Google Earth called Google Earth Pro for business users. That version has some new features (e.g., better printing, advanced import support, etc.) but uses the same imagery so it's generally not worth the annual cost for the casual user.
Usually several months after imagery is taken before it is available on Google Earth. It takes months of post-processing to incorporate new imagery into the Google Earth database. For that reason you almost never see imagery newer than 6 months old.
Google Earth is a graphics intensive application. If you run Google Earth concurrently with a number of other applications that consume large amounts of memory and/or video driver resources then your computer will run slowly. In some situations running Google Earth in that scenario could lockup/freeze your computer (e.g. Blue-Screen-of-Death) but concurrently running any combination of graphics intensive applications or computer games could in fact crash a computer. Similarly, if you plugin in an air conditioner, power-saw, and HD TV all running on the same outlet in your home then likely you're going to blow a circuit. Same as running applications like Google Earth with other like applications at the same time. If running Google Earth makes things run slowly then you have the option to exit the other applications and run Google Earth alone or install more memory on the computer.
The starting current of any electrical equipment which is 6 times more than that of the full load current. ex: full load current = 5 A the starting current will be 5*6 = 30 A.
Imagery UpdatesGoogle Earth imagery updates usually happen about every 2-3 weeks but the updates are not to the entire globe but to cities and regional areas often in multiple countries. Google provides a KML feed to show where the updates are located and also has a notification service to receive alerts when your selected areas have been updated. See related question for details.Google Earth Software UpdatesGoogle Earth software is usually updated several times a year with a major update (e.g. 6.2 -> 7.0) about once per year.
I guess it is free to use however, you cannot distribute it on your own. In free version you cannot integrate your GIS data but there are another versions like Google Earth pro and Google Earth enterprise.