Opera and Expedia
My father tried to book a flight using Expedia. Would not work well with Opera. His complaint to Expedia's tech support resulted in TS sending him a long knowledge base article explaining the technical ramifications of Opera's Javascript and DHTML support, none of which is relevant because Expedia is coded to work best with IE and not well at all with anything else.
How surprising, since they're a Microsoft spin-off...
After commiserating with him (I also use Opera and thoroughly enjoy it - enough to buy the commercial version), I promised to look into which companies are MS-funded or -owned, such as Expedia. I might also see which ones MS's CEO owns personally.