no JTAG connector
That's correct. Even if you use a makefile you still copy the result to the Mbed "disc" and the bootloader takes over. In itself I have no real problem with that but there should be alternatives.
I think they want you to be part of the Mbed collective.
From what I've seen the online compiler is good in many ways, I think you can just grab a serial setup library etc and it's whipped into you project, all rather seamless.
But it's very hard to find out about this stuff because the forum is closed. I kid you not, you have to be an Mbed owner to join (serial # is needed). You can browse but tough luck if you want to ask a question before buying a board.
Is it any wonder there's so much mis information about the system?
As for LPCXpresso that's entirely different, all open and available in three flavours from small LPC11xx to the ... well how about a quote from the "Getting started" guide
?
LPC1100: LPC1102 LPC1111/101 LPC1111/102 LPC1111/201 LPC1111/202 LPC1112/101 LPC1112/102 LPC1112/201 LPC1112/202 LPC1113/201 LPC1113/202 LPC1113/301 LPC1113/302 LPC1114/201 LPC1114/202 LPC1114/301 LPC1114/302 LPC11C12/301 LPC11C14/301 LPC11C22/301 LPC11C24/301 LPC11U12/201 LPC11U13/201 LPC11U14/201
OM11049: LPC1114/302
OM13014: LPC11U1?
OM13012: LPC11C24
LPC1200: LPC1224/201 LPC1224/221 LPC1225/301 LPC1225/321 LPC1226/301 LPC1227/301
OM13008: LPC1227
LPC1300: LPC1311 LPC1311/01 LPC1313 LPC1313/01 LPC1342 LPC1343
OM11048: LPC1343
LPC1700: LPC1751 LPC1752 LPC1754 LPC1756 LPC1758 LPC1759 LPC1763 LPC1764 LPC1765 LPC1766 LPC1767 LPC1768 LPC1769 LPC1774 LPC1776 LPC1777 LPC1778 LPC1785 LPC1786 LPC1787 LPC1788
OM13000: LPC1769
LPC1800: Coming soon
LPC2000: LPC2109 LPC2109/01 LPC2134 LPC2142 LPC2362 LPC2929
LPC3000: LPC3130 LPC3250
LPC4000: Coming soon
As you can see it includes the 1768 that the Mbed uses and with Xpresso you get full SWD/JTAG debugging and the programmer/debugger half can be snapped off to be a generic LPC programmer.
Anyway I don't want this to be a "bag the Mbed" post, it looks like a great platform and I could still get one but I think I'll be going down the Xpresso road. With my background it has a better "seat of the pants" feel to it but others will think incorrectdifferently 
Do you think it's possible to create a debugger than would work for the normal Arduino Audience?
What sort of debugger? For which platform?
Rob