Re "What the transmitter 'sees' on its data pin is what the receiver outputs on its data pin. If you can configure the UART module on a PIC, you have an instant wireless data connection"
There sometimes is some confusion about what that actually means. Certainly, in the middle of a data packet, if the line on the input goes from low to high, the line at the other end will go from low to high.
What isn't entirely clear is how the device handles DC. If you have a low on the input that lasts for 10 seconds, do you get a low at the output?
I'm not sure ASK works like that, and the test would be whether you could use the module in place of the dowload cable and handle the Break command properly. Even FSK can be a bit vauge - are you talking about shifting the frequency up in the megahertz to send 1s or 0s, or is the shift down in the audio range like the way old dial up modems used to work?
The other issue with modules is what you get on the receiver when there is no signal - do you get a low signal, a high signal or white noise?
I suspect these modules are just fine for 99% of picaxe applications, as long as you do all the tricks that manuka et al suggest - eg putting Us before the packet, keeping the packets short, happy to live with a picaxe hanging in serin etc.
I have yet to find any module that can replace the download cable, though there must be one out there.
Last night I managed to send an entire copy of Microsoft's original Basic, which is a 23k file, from one board to another at 4800 baud, and then get it back again intact. But there were a few tricks along the way - using the Hope RF modules, working within the parameter that they send data in packets of 32 bytes, putting in delays when needed, and using the Xmodem protocol which breaks files up into 128 byte blocks with checksums etc. So even smart modules like the Hope ones are not true transparent replacements for a cable.
For picaxe work though, where the packets are less than 15 bytes and you can put UUUUU at the beginning, these modules would be perfect. Anyone care do do some range tests?