The "Find My" function requires active 3G. If you think about it, it's essentially useless without 3G.
the above statement is not correct.
if you have WiFi and 3G turned off and try to use Find My iPhone, the service says your iPad can't be located (as expected).
If you then turn on WiFi only, and do any kind of network access on the iPad - e.g. browse a webpage - it will take a few minutes, but then your iPad
will show up on Find My iPhone. this is of course assuming your iPad is associated with your Mobile Me account already.
I just tested this with my 3G iPad (3G is turned off, and I don't have a current data plan enabled anyhow). Find My iPhone could locate my iPad's location correctly once I established a WiFi connection.
p.s. another poster mentioned that Find My iPhone doesn't report the last known connection. this is also not entirely true.
it seems if your iPad was online and located by Find my iPhone, then goes offline - your last location is remembered (for how long, I'm not clear). Again, I just tested this - after disabling my iPad's network connection and relaunching Find My iPhone, after several minutes of searching it fails to connect, shows the red dot, but still shows the last location on the map and how many minutes it's been since last located (now about 30min in my test). Maybe the last location will be lost after a longer period being offline, I've never checked that...
UPDATE: with additional observations
Find My iPhone remembers the last known location, at least as long as the next day (haven't tried longer)
but here's another interesting thing I noticed:
1. at home, after being located by Find My iPhone, then going out of WiFi range (3G off, not connected to any known WiFi router), then iPad gone to sleep...
2. next day, go to work, iPad still asleep in briefcase, no WiFi routers online that the iPad can connect to...
3. Find My iPhone reports last known location (at home, 10 hrs ago)
4. now, power up an AP Express WiFi router the iPad has previously connected to, and with iPad STILL ASLEEP...
5. re-run Find My iPhone - and now the iPad is correctly located at it's new location
note:
the iPad's location was found while still asleep - just that it was in range of a previously known wifi router
I wonder if this would work if a sleeping iPad was brought in range of an unlocked but previously unknown WiFi hotspot? ...