I wrote a userscript that generates a network wide flag summary for you. (It doesn't list single flagged posts though). It's available on StackApps.
If you are logged into the Stack Exchange network and you have this script installed, you can visit the new flags tab in your Stack Exchange profileflags tab in your Stack Exchange profile.
The script scans your network profileyour network profile for all Stack Exchange accounts you created. For each account it tries to access the flag summary page. Since that page is private, i.e. only visible to you (and mods), you need be logged in. From there it extracts the flag summary of the individual site and sums it all up in a generated table.