Hi,
After all, I was ignoring all of those all important handshaking signals, right?

ALE, PSEN and EA are not "handshaking signals". They must be set with correct levels to involve MCU in uploading mode. Read about Hardware Conditions of bootloader.
Indeed, at first time when you get a part from a factory, it has "bootloader jump" bit set. And so you do not need to do additional signals` setup. But only for first time! After you have loaded hex file into device and then reseted this bit (it is required to run your program), it will not be possible to go into boot mode anymore without hardware conditions (okay, with some software framework it may be possible, but it is not a question of matter we talk about for now).
How it looks at my projects:
- EA is tied to Vcc.
- ALE is not connected at all;
- PSEN is connected to grounded switch (you know it: pullup resistor is presented as well);
- RX/TX are connected to COM-port via MAX232.
So what I do:
- if I need to upload my program into chip then I connect PSEN to GND with switch then power on and use FLIP;
- if I need to execute my code then I switch off PSEN from GND and just power up.

Regards,
Oleg