For them there's business card scanners. The latest is the recently announced MobileOffice S800 from Plustek Technology Inc. It's powers by its USB connection, and is only 2x4x1 inches, making it suitable as a laptop accessory. The list price is $129.
It amounts to a tiny black-and-white or grayscale 600 dpi scanner, which is sufficient for text recognition. It is rated at 10 cards per minute.
The interesting part is the software, which is touted as being able to pick out the contact information that the business card contains, including styles used in 50 different countries, and present it in a number of data formats. These include (among others) Excel, Outlook, ACT!, GoldMine, Lotus Notes, CSV, and vCard.
The trick, of course, is what you do with the data after that. Electronic rolodexes (also known as contact managers or address books) are vastly superior to the manual kind, but either is probably better than nothing. Of course, you can't be nosing through your files during a meet-and-greet, so keeping some things in your head is unavoidable.
In other words, technology is never the complete answer.