Make systemd user service depend on system target

Forget the network.target. man systemd.special says:

network.target
       systemd automatically adds dependencies of type After for
       this target unit to all SysV init script service units
       with an LSB header referring to the $network facility.

So, this target is primarily a compatibility hack for SysV init scripts.

Assuming that your network connection is handled by NetworkManager you were of course right to depend on this target because NetworkManager.service defines Before=network.target. But this only means that NetworkManager has been started, not that the network connection is actually established. That may take a while (dhcp roundtrips, wifi handshake, etc.) and is entirely the business of NetworkManager. At least on my system (F18) there is a service called NetworkManager-wait-online. It uses the nm-online utility program to block until there is an active connection established. Try to Require, Before that in your Unit definition or use that tool on its own.

I was having the same problem, with a userland backup script that needs access to the internet. I solved it by adding ~/.config/systemd/user/wait-for-network.service that just pings google.com until it is reachable:

[Unit]
Description=Ping a server on the internet until it becomes reachable

[Service]
Type=oneshot
ExecStart=/bin/bash -c 'while ! ping -c1 google.com; do sleep 1; done'
TimeoutStartSec=60s

Then I made my backup script depend on it like this:

[Unit]
Description=...
Requires=wait-for-network.service
After=wait-for-network.service

This works regardless of whether you use NetworkManager or some other means to establish the connection.