Surprising, yes. Heck, even Mugi is surprised!
A seller named euf02us placed a guitar signed by the K-ON!!'s voice cast on auction on Yahoo! Japan on January 5, and a user placed a 9,999,999,999 Yen (US$120 million) "bid" on Monday morning!
People who spent a certain amount at LAWSON stores could go online with numbers from their store receipts to see if they won prizes. By the second day of the campaign, LAWSON's computer and mobile phone home pages received over 1 million accesses in one day, and the company's website was temporarily unreachable for many users.
The campaign's top-level A Prizes were five replicas of Yui's guitar signed by the five cast members who voiced each member of Ho-kago Tea Time! Each guitar also came with a limited-edition hard case (with an imprinted HTT logo and key), set of clear stickers, shielded cord, tuning wrench, soft case, manual, and warranty certificate.
Source: Kyō mo Yareyaku via Anime News Network