dsPIC33Fs are actually quite nice, and offer quite a lot of processing power (but less than any given Cortex-M4). Unfortunatelly they suffer from all sorts of "Microchip-nesses" such as shitloads of silicon bugs, shitty compiler and bad libraries. And on top of that they are in the same price range as ARM stuff.
I agree.... we need to remember that the dsPIC is quite fine for lower end applications such as signal conditioning and basic low bandwidth software radio's. Its quite capable for example of taking a 6KBPS sample, demoding it and filtering it using an fft. Of course its a relatively small fft. So thats the kind of app you should be thinking about for them. They are not complete toys and do integrate things like I2S for codec comms which some of the plain vanilla CPU's dont. I generally view them as better than an NXP LPC ARM7.
On the other hand if you want to crunch 50MBPS data you wont get by with a dsPIC, you'll need something like a TMS320C.
You can do similar things on an ARM of course ie ARM9/11 and above. This is what we currently do at my work. The only caveat I would add though is that while general purpose processors can often provide decent CPU performance we've found we need some fairly high current consumptions to get the performance we need because they are working hard (generally clocked alot higher for starters). This will be a real issue in future as customers complain about battery life.
The other alternative of course is to implement an algorithm in a FPGA using VHDL or Verilog. This is something we used to do as well but again, power is an issue. The Xilinx part we used was so hot it was untouchable. (some of the ARMS (OMAPS) we've used were similiar)
With regard to compilers, my personal opinion is that none of the chip makers produce decent compilers. I use a third part compiler for the the dSPIC. MPLAB works but IMO just takes too long to get things up and going, has poor documentation and support. I use CCS for that chip. Similar story with the ARM. Of course for the FPGA's there are no real 3rd party alternatives for development tools so you are kind of stuck (and screwed) with regard to environments. I generally prefer to avoid FPGA's for this reason, plus cost and power concerns. Compilers are one thing I will fairly happily shell out dollars to buy - and often play a part in the final choice of device.
Edit: I'll add one last thing - maybe a plus for an arm. I'm currently working on a radio that will use linux as an OS. As soon as you want something like that (ie connected to the internet, running servers and can be reconfigured) the ARM is the only way to go.