My company switched over to them for a short while because the rates were better than Fedex, but we quickly switched back. We are an civil engineering firm, and we inspect cell phone towers for all the major companies (Alltel, AT&T, Verizon, etc.). If we don't get our reports out to the on time, they may have to shut down the tower, costing them money and when that happens, we don't get paid. When we were using DHL, we found that they don't work on the weekends, and if you need a package that goes out Friday to be somewhere by Monday, they drop it in the USPS box. Instead of arriving Monday, some arrived Wednesday, some arrived Thursday, and one got lost in the mail and didn't show up for almost a month. When some didn't show up Tuesday, we immediately shipped out duplicates overnight, but we still lost money on 5 different towers because they just dropped it in the parcel post as well as hurting our relationship with clients.
Just my personal experience (I am the Admin Assistant in charge of packaging and shipping reports, as well as other things).
-Rose