I don't recommend turning on and off the service manually. Why would you want to cripple a program and for what purpose? If the service is not running many things will not work as it depends on the service for most functions.
Linux2009, have you been turning off the service? Could this be why you are having problems with updates?
Here is important info about the service and why it is a critical part of the Ad-Aware program
This applies to the Ad-Aware 2008 as well as the 2007, since the Ad-Aware 2007 was introduced and it is still part of Ad-Aware 2008.
Why does Ad-Aware 2007 run as a service?
http://www.lavasoft.com/support/faq_aaw2007.php#15THE AD-AWARE 2007 ARCHITECTURE
Ad-Aware 2007 consists of two main parts, the Service and the Graphical User Interface (GUI). The GUI is the part of the program a user sees and needs in order to interact with the program itself; it contains menus, buttons and other controls that are necessary for a user to run the program.
User action is passed from the GUI down to the Service, which contains the core functionality of the program. The Service executes the action, and then reports the results back to the GUI, where it is presented to the user.
What Is a Service?
Services are Windows applications that are launched at system startup and then run in the background, not visible to the user.
What is the Benefit of a Service-Based Approach to Malware Removal?
Malware that emerges today is increasingly complex, displaying wildly varying behavior and operating on many levels in the system. In order to stay a step ahead of these ever-changing security threats, an anti-spyware tool needs to be more powerful, multi-faceted and flexible than ever before.
The implementation of Ad-Aware 2007 as a Service facilitates this needed power and flexibility since a service runs with elevated rights on the system. This means that the user can work in user-mode while the Service maintains the elevated rights it needs in order to properly detect and remove malware infections.
How Does This Affect Resource Use?
During a scan, the CPU use of the Service will vary parts of the scan are labor-intensive and require a lot of processing power, which can make the computer's performance sluggish. Other parts require less computing power and have little impact on the overall performance of the system.
When the service is idle, virtually no CPU power is required, making the impact on system performance negligible.
As for memory use, the service does require a bit of memory, most of which is needed for storing the threats in the Detection Database. It is important to note, however, that when the Service is not in use, the lion's share of this memory is paged to the Swap file. In non-technical terms, this means that the hard drive is used to store data that is not currently in use, and then retrieves the data when needed, which makes the actual working memory (RAM) available for other applications.
Just as many other security products do...(a-squared, CounterSpy, SpySweeper come to mind)