I only have access to a 600x600dpi cannon, got it for £25 off ebay with a new toner cartridge. As for results? The toner seems fine with most papers (glossy, magazine, blue p'n'p, even managed a few boards with cheap plain stock paper) but the '600 dpi' has posed a problem for 0.5mm pitch IC's. I have no idea if 1200DPI really would be twice as good, as I printed off a design on a friends printer (1200x1200) and it was still a bit iffy.
One thing I have noticed about my cheap printer is accuracy. I spent a long time trying to work out why its scaling was slightly off. For a pin header, 2x20 (40 way) it printed out slightly smaller, so by the 30th pad, the hole 'should' have been where the pad ring was. Any board smaller than 2" square, was within tolerance.
Turns out this was nothing to do with software scaling (turned all that off) but was merely the accuracy of the printer at the edges of the paper (!!). Printing off a design in the center, portrait, it came out spot on. So beware people, always print off a test pattern with a grid just to see whats going on and if your printer has any weak points with accuracy.
I cannot say this is the case for most cheap printers but I have never seen this mentioned before.. maybe I got a lemon eh?
Other than than, 8mil track/spacing is doable, especially with blue p'n'p.
As for board material, I assume you mean FR4? theres also FR2, and CEM1/3 which are much kinder to your tooling. All of which can be had off ebay. (from shops, not second hand lol).
Blueteeth