Windows XP Pro SP3 (up-to-date).
I also experienced the problems with add-ons disappearing in Firefox 3.5.3/4 and wasted ages trawling for solutions. Having fixed that, the many reboots involved have confirmed that some icons now consistently fail to appear in my taskbar after a restart or a shut-down and reboot.
For example, the volume control icon is not there; I have to go into the control panel to disable and re-enable the icon. Netmeter is running but has no icon. I have to kill it and restart it. All this is irritating and time consuming - and costs me money in lost work time. This has cost me - in real dollars - far, far more than the purchase price of NIS 2010.
My guess is that efforts to improved the load time of NIS mean it is preventing other tasks from completing. I have a brand new computer with a quad processor and 4G of RAM (even if it's not all usable in 32-bit XP).
As a software developer, I understand the concept of a limited release of a major upgrade. However, our guinea pigs are carefully selected; they know that's what they are, and we keep in constant contact with them.
I've been a user of Norton products since the mid 1990s. At this moment I'm a very unhappy user.