I would like to add an option to the View menu, 'Fast rendering'.
It would also be great for when I'm working on projects where I have a lot of effects (currently doing one with a bunch of different paths all have gaussian blurs). I could do a fast render where it will not render the blur perfectly or something while working, reducing lag and making feedback snappier while using, and then at the end of the day I can turn the feature off see how everything looks.

Custom profiles for this. A list of every effect, whether built-in or plug-in, with a switch to disable it for this particular performance level. I use a lot of effects that can produce an *apocalyptic* number of paths and it would be great to be able to turn them off without actively going into a bunch of appearance stacks and toggling their visibility.

You might also want to upvote this request:
Return greeking of vector graphics
http://illustrator.uservoice.com/forums/333657/suggestions/32403922

I’d add to that.

1 . Unlike in InD with it’s abstract 'Typical, Fast, High' I need to also see actual VALUES behind these. Something like 'Fast (18 ppi)' (the number is just a random one).
2. I think we might benefit from the ability to set it to a custom one, similar to Raster Effects’ Resolution
3. Perhaps we might need to link this both?
4. Obviously this value should NOT affect exported images. This is interesting, since Effects’ Resolution does... needs thinking
5. Definitely we need hotkeys slots for all, including the last used custom one.
6. Surely we need a hotkey slot to toggle two las used states
7. In InDesign the actual resolution is related to the image's actual resolution (there were some experimentations). Long story short — it hardly feels OK, so make this right.

I'd like to have a setting for preview quality like InDesign.

We constantly work with many linked .ai files in one main .ai file, and it leads to performance issues. I believe they could have better performance is there was an option when we get rasterized previews with resolution options, instead of Illustrator having to redraw the vectors every time we navigate the file.

I'd like to set image quality, it will fasten my workflow, since sometimes i work with large and heavy image, but illustrator it becomes very slow with big raster images.

Yes I will vote to make this happen, just like a proxy in Premiere Pro where you can use to make a faster workflow, and not crash Illustrator like if you have a very complex vector background that is you're not going to edit often. This is a really big help.

That's exactly what i was going to put here. This would be awesome. And it would put an end to those errors when illustrator stops saving the **** file.

I really like in after effects and premiere how you have the ability to use proxies. I do a lot of large signage and I have to import very large PSD files, illustrator is extremely slow and crashing a lot. I have sort of accepted it as a way of life, saving my files regularly, but it would be nice if large images worked better in illustrator. Maybe something like InDesign would be good. In InDesign you can choose different levels of preview quality. InDesign is wicked fast because of this.