I've been running Nod32 version 3 on my system for about a year now and so far I've been very happy with how little effect it has on the system performance. On my older AMD XP3000, applications appear to launch just as quick with the virus checker running as with it disabled.
The following is some stop-watch timings I carried out last April on the same day when my system was very cluttered (running various services). Unfortunately, I forgot to take note of the software versions I was using as I was doing this for my own use to see how Avast compared to the Nod32 trial version at the time, but it gives an idea of how they compared at the time. With how often Virus checkers update their versions, these timings may no longer be that accurate now:
Timings - No Antivirus / Avast Home / Nod32 Av:
- Boot from BIOS beep to Desktop icons show - 38s / 46s / 40s
- Boot from BIOS beep to Desktop & HDD LED stops blinking - 1m21s / 1m43s / 1m12s (AVG : 2m00s)
- Microsoft Word 2003 - 1.7s / 2.6s / 1.5s
- IE7 launch until Google home page shows - 3.8s / 4.6s / 4s
- Gimp 2.4 - 8s / 13s / 8.4s
- Thunderbird - 7s / 11.5s / 7s
- OpenOffice 2.4 Writer - 8s / 11.7s / 7.4s
- Newsrover - 6s / 6s / 6s
- Firefox launch until Google home page shows - 5s / 6.8s / 5.4s/
- Read all files in System32 dir (DOS: copy * /b nul) - 25s / 23.4s / 30s
- RAM usage (after full boot): 383MB / 480MB / 412MB
I do remember AVG having longer timings than Avast, especially for the OS boot time, but unfortunately I lost the timings for the application launches. On the other hand they were likely based on AVG Free's earlier v7.5.
Unfortunately Nod32 does one irritating drawback, in that there are some executables it really struggles with while copying. For example, the System Information for Windows (SIW.exe - 1.5MB file) executable takes 10 seconds to copy from one drive letter to another on that AMD system. During this time the ekrn.exe process (part of Nod32) shows 99% CPU usage in the task manager. At least it doesn't affect the launching of the affected software, for example, SIW will launch straight way.
For some reason nod32 AV Version 4 doesn't get on well with Thunderbird on my system, so I've stuck with version 3 for now. At least unlike some AV companies, they just charge for the subscription and not for each new version also.