I suppose if we figure out how to make click-to-pay work for both the "I'm using an online wallet service" and the "I'm using the client" cases, then users won't have to know how to copy&paste addresses and human-type-able addresses won't be critical.

RE: DoS resistance:  please DO keep thinking about it; I'm not a networking expert (in fact, if you know any networking experts, see if you can get them thinking about it....).