When the Mrs and I started getting serious about our bitcoins, we bought a laptop only to be used to mine bitcoins and perform bitcoin transactions. We never use it for anything else and keep it updated. Never had a problem with any site or service, but then we dont allow any of them to hold any money or coin for more than a few hours. We use it immediately and either send the coins to our own bitcoins wallets, or we send the cash to our bank - which is a bitcoin-only account. Also, when signing up for sites and services, use long passwords with lower case, upper case, numbers, and special characters. I use KEEPASS for name/password combinations that are long, then its simply a matter of copy and paste. Lastly, we have our laptop hard drive encrypted with truecrypt and have many backups of our wallets saved to hard drive, memory cards, cds, usb drives, and online in the cloud a few places, and of course we have copies cached in all of our online email accounts.