The frequent example is pretty crazy. I work for a small software company. We have a low-cost product that we sell that uses actual license keys we have to generate. The task of actually generating those keys, and thus doing the formal "this is your delivery" emails, falls to me b/c it involves SQL. Takes 2 minutes, so nobody wants to spend the time writing a front end for it, etc. Familiar story I'm sure.
Anyway, so I send out the fulfillment mails. Boss always gets a copy. They always have a PO number in the subject line. He'll search his Outlook, and VERY VERY OFTEN Outlook can't find it. I'll search MY mail in Mail.app, and can forward it back to him in seconds. I've watched him do it. I've duplicated the failure myself -- I have true-blue Outlook running in a VM, bc sometimes you need it for calendar stuff -- and it just plain fails. A LOT.
It sure seems like "search" would be an important part of a good email client, but Microsoft appears to disagree.
Because I have some pretty large mailboxes on my Mac, and Mail.app searches/indexes them like a champ. The search, in fact, is what KEEPS me on Mail.app -- it would be way more convenient for me professionally to surrender to Outlook, and Mac Outlook is really not bad, but holy hell is Outlook's search GARBAGE compared to the Mac client.