How do I check if an app is a non-system app in Android?

I am getting a list of ApplicationInfo Objects with packageManager.getInstalledApplications(0) and attempting to categorize them by whether or not they are a system application.

For a while I have been using the technique described here, however after seeing that in my application, some of the apps were not in the non-system apps list (such as Facebook, which when available asks the system to install itself on the SD card). After next reading the actual documentation for ApplicationInfo.FLAG_SYSTEM, and understanding that it doesn't actually filter system apps, I am now looking for a new approach.

My guess is that there is a large gap between UIDs of System and non-system apps that I can gather to make this distinction, but as of yet I have not found an answer. I also looked into other flags, such as ApplicationInfo.FLAG_EXTERNAL_STORAGE, however I am supporting API 1.5.

Does anyone have a real solution to this (not involving FLAG_SYSTEM)?

Well, it's a sloppy solution in my opinion (what if /data/app isn't the apps directory on all devices?), but after a thorough search, this is what I have come up with:

for (ApplicationInfo ai : appInfo) {
    if (ai.sourceDir.startsWith("/data/app/")) {
        //Non-system app
    }
    else {
        //System app
    }
}