Since I discovered this:

http://letsmakerobots.com/node/5916 

all has changed! I was blind, but now I can see. And I can program!

On Picaxe, in order to send with these modules, use this code:

testsender:
for b0 = 0 to 255
high 3 pause 3 low 3 pause 1 serout 3,N2400, (85, 85, b0)
pause 200
next b0
goto testsender

and to recieve, use this code:

testreciever:
serin 7, N2400, (85,85), b0
sound 0, (b0,10) low 0
goto testreciever

- Of course adapted to your own setup etc.

The important parts here are:

high 3 pause  3 low 3 pause 1 serout 3,N2400, (85,85...

and

serin 7, N2400, (85,85...

Because with that combination all together, the reciever is left most happy in all states, and the result is 100% rock steady. Like in not a single bit lost in a thousand!

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Bonus tip:

A) Hook up a speaker to your MCU

B) Send sound to it in a loop

C) Take off the speaker, and hook up the sender

D) Power up the reciever, and on the out-pin, hook up the speaker (and other wire to ground on the reciever)

Now do you hear sound from the reciever, punk? If not, you can rest assured that your recieving MCU will not get any signal either :)

Yes, you can start your own little radio station with these ;)

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(Note that this post has changed, some of the comments below may be from earlier)