This is from a topic I posted on a mbed course:
I was under the impression it (mbed) was a lot like Arduino where it's a nice idea and great for tinkering, but a really bad idea to use to launch real products with (so far as hidden functions and inefficiencies).
I do not know anything about mbed but I keep think of trying to learn something about MCUs using mbed. I know it is a good idea because of the online IDE and compiler but is this true about mbed ?
Any time you use a library, you have to wonder 'who wrote this thing?' and 'did they have any idea how it should be done?'. Some libraries are better than others.
The online IDE works well. You can, if you wish, rip the entire project to your local machine (including libraries) and use any other enviroment that supports the language (based on GCC) and the device. I have done it with Rowley Crossworks and everything worked fine.
You really don't want to write your own network stack if you can avoid it. The mbed stack is based on the very well establish lwIP stack. The only thing the mbed folks did was add the device driver. It is plug-and-play but you have to use it in a super-loop. Examples abound!
The original mbed, the only one I have used, is a 96MHz LPC1768 32bit ARM with Ethernet and USB capability. It has 512k of Flash and 32k of RAM plus another 2 banks of 16k of RAM.
https://developer.mbed.org/platforms/mbed-LPC1768/The average Arduino is a 16 MHz 8 bit AVR with no Ethernet or USB. It has 32k Flash and 2k RAM (ETA: Arduino UNO)
In concept,both systems hold your hands, if you need it. You can use their libraries if you wish or you can deal directly with the hardware.
There is a downside to losing some of the mbed IO ports due to a lack of pins in the 'stamp' arrangement. If you did a bare board, you could have all of the pins but you would lose the bootloader feature.
Performance wise, there is no comparison between the Arduino (think Yugo) and the mbed (think Ferrari). But when I want something down and dirty, the Arduino is laying on my bench. Go figure...