The problem is that it's too slow to be used as an actual development computer, so you have to write your code on another computer and then copy it over to the pi.

"Too slow"? Thats a very consumer-centric point of view. Compiling onboard is quite sufficient for most small projects, and really .. its a matter of patience, but for sure its quite usable. For those more used to the fat-IDE approach, where everything is done for you at a few clicks, its certainly not interesting .. but if you want to get really familiar with software development, doing things onboard the rPi can be a very effective way to develop. The so-called limitations of the device can also work in your favour: write smaller, tighter, leaner modules, and you don't have to wait so long in between compiles.

Not to mention that there are plenty of ways to use the rPi that don't require compiling. I myself use an onboard Lua environment, which just plain rocks .. ssh in, open up vim, edit Lua .. run in another terminal. Quite a comfortable environment, and I hardly even care that its on a 'small/slow CPU' (after all, I lost interest in the speed race decades ago. Those of us who grew up building the Linux kernel on MHz-class machines don't feel your pain.)

Hooking the Pi up to a monitor and using it to actually edit on is extremely slow, once you've loaded an editor a browser a couple of terminals and maybe an MP3 player it's a crawl compared to devices anyone is used to in 2014.

I don't, ever, even think about lag in between :w and :ma .. these things just plain work. For everything else, there's 'cscope -R -s /usr/include #&etc'.

For pure C/C++ projects, I use cscope+vim+make on the rPi. For Lua projects, just vim .. and a few judicious 'watch ./ make' style sub-cmds in another shell.

GUI editors are not your friend, I accept that. But there is more beneath the hood than such a dilemna as not enough RAM to load bitmaps ..

Check out sshfs or similar user-mode filesystems to make the Pi look like a drive. Cyberduck is another tool that has a decent file explorer UI around SSH/SFTP and is cross platform.

If you're writing C/C++ you can set up a cross compilation tool chain to write and compile code on any Linux machine. It's a pain but there are lots of blogs posts and guides on it.

Sure, but I mean you already need another computer in order to program the pi at which point you already have a computer that can run programs without the pi.