a great bulk of this is NOT online, including roommates stealing checks, trash pickers, etc.

Get a cross-cut shredder- now about $20 on sale
shred any credit card or mortgage stuff addressed to you

I can identify phishing instantly. I have my own domain, with a 'catch-all'. Paypal, my bank eBay all go to specific email addresses that no-one else has, e.g. bidders@mydomain.com or myaccount@paypal.com.

This way, if 'supposed' email from ebay is not to this email address, I delete it instantly (sometimes I'll forward it to their spoof or abuse email accounts).

scan constantly for keyloggers. they sneak on even to the best protected systems due to holes in browsers.

http://www.trendmicro.com/spyware-scan/free_spyware_scan.asp

is a good online free scanner for spyware

in restaurants, don't hand the person your credit card. alot of theft comes from restaurant employees with card readers that capture your credit card info at same time they swipe it thru restaurant's credit card system.

instead pay cash for meals under $25 if you can. I'm not advocating carrying alot of cash which has its own problems.. if you pay with card, give it to clerk at register always. best if you swipe it yourself in plain sight.

beef up any PCs you have with an outgoing firewall like zonealarm. get a $25 cable router so outside systems can't ping your PC. it fits between cable modem and your PC. Even has multiple ethernet out so you may not need a hub.

don't use wireless at home if you can help it, and turn on security if you must.

before giving CC# to online retailer,
check their ratings at:
resellerratings.com

(find the store box and type in website address, will tell you individual consuemr's exprience the website, also good to know if you'll ever get your order on time)

I pay electricity, cable, phone online which reduces checks that could be stolen in mail.

be careful but don't let it rule your life worrying about it.