Does the macbook use the internal harddrive when booting from usb and when fully booted?

Then I wonder what might cause the system freeze ups. I had a system freeze up just now after two hours of running from the bootable USB. When booted from the internal SSD it freezes up much more frequently (within every 1-5 minutes) after its booted. I checked cpu and system temperatures and they are all fine (below 50 degrees celcius).

I just verified the drive and its permissions from Disk Utility. Some permissions where off. I have fixed them with the Disk Utility. Do you recon this might cause full system freeze ups? I will do a test run and find out.

What i'm doing when it freezes is totally random. I am not having any programs open, but for example just clicking on the apple icon or starting up safari, there seems to be no specific program that crashes it. I'm still running without a freeze up after I fixed the drive permissions with Disk Utility. But here is Etrecheck;

Hardware Information:

MacBook Air - model: MacBookAir2,1

1 1.86 GHz Intel Core 2 Duo CPU: 2 cores

2 GB RAM

System Software:

OS X 10.8.2 (12C60) - Uptime: 0 days 0:9

Disk Information:

APPLE SSD SM128 disk0 : (121,33 GB)

disk0s1 (disk0s1) <not mounted>: 209,7 MB

MacBook Air (disk0s2) /: 120,47 GB (106,36 GB free)

Recovery HD (disk0s3) <not mounted>: 650 MB

USB Information:

Apple Inc. Built-in iSight

Apple Inc. Apple Internal Keyboard / Trackpad

Apple Computer, Inc. IR Receiver

Apple Inc. BRCM2046 Hub

Apple Inc. Bluetooth USB Host Controller

FireWire Information:

Kernel Extensions:

Problem System Launch Daemons:

Problem System Launch Agents:

[failed] com.apple.afpstat.plist

[failed] com.apple.mrt.uiagent.plist

Launch Daemons:

[not loaded] com.bjango.istatmenusdaemon.plist

Launch Agents:

[loaded] com.bjango.istatmenusagent.plist

User Launch Agents:

User Login Items:

iTunesHelper

3rd Party Preference Panes:

None

Internet Plug-ins:

JavaAppletPlugin.plugin

QuickTime Plugin.plugin

User Internet Plug-ins:

Bad Fonts:

None

Top Processes:

It just crashed for no apparent reason. I try'd clicking on Finder and the system freezes, only rescue is shutting down the whole system by holding the powerbutton. Only running program was EtreCheck. I'm really wondering what might cause it. Does the report ring any bells?

I can't get into diagnostics. I'm holding 'D' while booting but nothing happends, I have a wireless connection. What am I doing wrong? I want to do a hardware check.

I did the hardwaretest via an iMac over airport on my Macbook Air as suggested in the link you provided, no hardware failures came up. Does this guarantee that the hardware is working properly? Note that I did not do the 'extended' test in the hardware test.

I will do the extended test tomorrow and see what happends. Thanks for your help so far!

Somehow the hardware test won't start up, the wifi seems unstable. But I managed to do a fresh install after formatting the SSD, it seems to be much more stable now. It froze up only once during the whole day. But still i'm not statisfied with the result. I might bring it to an apple store and see. (it's outside warranty).