For me, the LowRider rack was a game changer. A rack you could put on a fix gear and still be able to go up hard hills loaded, out of the saddle; tugging the bars, twisting the frame and rocking the bike with every muscle you had. And the only change in bike handling was that it was (however much you were carrying) harder.

Yes, those racks weren't perfect, Every singe one I owned eventually broke at the dropout. Not dangerous; I usually learned about it when I went to remove the rack. The Jadd (sp) and another post-Blackburn rack have each outlasted several Blackburns and are going strong. But without Blackburn, they probably wouldn't exist.