I was born in 1981, so obviously I don't remember the awesome DX that some of you have heard - especially those of you who personally remember the night KDKA first signed on.

However, I have gotten little glimpses of it, occasionally...
Before the X-band got crowded, I could hear the DFW stations here near San Diego, CA.
I can fairly regularly hear the LAX TIS on 530 in the daytime, although recently it's been clobbered by a local caltrans TIS.
I've heard Albuquerque's 1240 Radio Disney once under my local 1240 KSON's unmodulated carrier, and I'm close enough to KSON so that when they do have programming on, I don't hear other stations in the background, or if they are there I don't notice it.
Also I've gotten daytime signals from 680 KNBR, 700 KALL, 810 KGO, 1530 KFBK and 1580 KMIK on more than one occasion.
As for 690 being so, so directional.... maybe they are, but I seem to not quite be in their null. XETRA (or is it XEWW now?) is 24.63 miles away at a heading of 199.64°, but puts in a good signal here - typically 63dBu on my Tecsun PL-380 in the daytime, and about 59-60dBu at night. XEPRS 1090 is typically about 47-49dBu here 24/7, though, and I sometimes get skywave/groundwave cancellation here, which leads me to believe they run their directional pattern fulltime. XEPRS is 26.11 mi away, heading 198.19°. When I've been in central california - Tulare/Visalia area (off Hwy 99 between Bakersfield and Fresno), the signal at night there on 1090 is usually considerably stronger than it is here at home. As for 1700 XEPE, they're a couple dBu stronger than 1090 on my PL-380, but the audible SNR is usually much better. XEPE is 15.62 mi away, heading 189.48°.
Besides all the stations that are authorized now, another thing that I think may be killing AM DXing, if it hasn't already, is all the QRN form man-made noise. I really wish the rules were tighter for things like that (while still allowing part-15 broadcasters and the like), but alas, it's not in my power to change it.
So has the static and man-made noise levels significantly increased since the 1930s, 1960s, etc? I've heard David say it requires a 10mV/m signal for a station to be heard in metro L.A. area. That sounds awfully high to me, as I have routinely been able to pull groundwave from stations for which I'm well outside Radio-Locator's predicted 0.15mV/m signal.... or am I the only one willing to listen to a signal with a negative signal-to-noise ratio?

Or, is suburban San Diego not quite as plagued with noise as L.A.? (The way I've heard the noise described in L.A. almost seems as if you'd be able to sit right next to a 50kW stick near downtown L.A. and not even hear their IBOC hiss. (didn't say "in" as I don't believe there are any 50kW IBOC stations IN "downtown L.A."))
Even if we didn't have man-made noise, though, there is still atmospheric noise, which I understand is produced by lightning storms. Ok, so I don't want to get into a religious discussion here, but I understand that before Noah's flood, and in the Garden of Eden, there were NO lightning storms anywhere. I wonder what listening to the radio below 30 MHz would have been like then? I wonder if it would have been possible for a 50kW groundwave signal on 540kHz to have global coverage?