Original questions: "When you give Awardwallet your passwords to your frequent flyer accounts, can they access your mailing address, credit card numbers (e.g., if you registered a credit card with any reward program or something like "dining for miles" if "dining for miles" can be tracked), upcoming or past itineraries and other such personal information?"

They can access anything that you can access by logging into your airline or hotel account. If those account pages show your full credit card number, expiry date and security number, then AwardWallet can see that information also.

They do seem to notice upcoming reservations, at least on AA.