This is a fascinating subject which deserves its own thread, so Ive split the posts off.
It all depends which satellites you want to see, how much illumination thay have etc.
Geosats can be seen with the naked eye occasionally as they flare up with sun reflection at certain times of year.
The International Space Station (much lower orbit than the broadcast sats of course) is an exceptionally easy naked eye object when the passes are favourable.
Iridium telephone sats can flare incredibly bright - Ive once see one cast shadows as its brightness raced up to mag -8! The iridium flares only last a few seconds though.