You can draw around 200 watts of power from a cigarette lighter socket. @ 230v that's about .6 of an amp, enough to run a few chargers etc. without a problem. If you do the maths that's just under 16-17 amps of power at 12v and most car cigarette lighters are fused at 20 amps. I can tell you thou, draw that much power for a sustained period on your cars loom and it will get a bit warm which is why you'll rarely find an inverter that's more than 150w to plug into your cigarette lighter, anything more powerful should definitely be wired directly to the battery terminals. Do note if you have a powerful inverter that you're intending to run high powered equipment from, it's unlikely your alternator will be able to keep pace with the rate you're draining the battery at and run the car and the inverter, so you will find your battery gradually runs flat. You also stand a risk of knackering your alternator through overloading it, I've done it myself before.
It's worth noting that inverters are not particularly good for running electronics as the cheaper ones use a modified sine wave which can cause issues with certain transformers and electronics. Saying that I've never had a problem, but I know people that have. It's also worth noting your 230v circuit coming from the inverter does not have an earth, so you should only use double insulated equipment (most chargers etc. are, but some laptop power supplies are not!) again the potential risk is low, but there is stil a risk.
@Bigjobs has the daddy of all inverters in the limo, it's a beast!
