sending your funds to a wallet consisting in an non-password protected URL is RIDICOLOUS
These services have their place. Instawallet is a brilliant service for introducing newbies to bitcoin. A newbie can have a bitcoin address up and running and making payments, literally within seconds. In this era of short attention spans, the Instawallet service is invaluable for spreading bitcoin adoption.
I frequently tell friends to visit Instawallet.org and quote me the address they see. Then I send some small change to that address. They immediately "get" bitcoin.
Yeah, in this era of short attention spans Instawallet is perfect to have newbie's coins stolen.
Tell your friends to use blockchain.info's My Wallet for their first pennies, is quite as immediate as Instawallet and much more secure.