Oh yeah, being able to use blind and buried vias, as well as via-in-pad and laser-drilled vias would be fantastic! However, the cost of those features are prohibitive for a hobbyist. Heck, just going from 2-layers to 4-layers is a cost increase of about 40%. I do think those features will trickle down to us in the future, as commercial products like cell phones and computer motherboards demand even more extreme requirements on PCB houses. As I mentioned earlier, 5 years ago as a hobbyist I could not get boards will less then 8/8 mil trace/space. No I can get 5/5 and the small vias needed to do the 0.8mm pitch BGA I need. It is pretty cool. And I have even been successful at soldering the darn things!
@BigEd: yeah, unfortunately the mixing of imperial and metric is pretty much something you have to deal with all the time. I think the industry is going metric, but we are in a transition period that will take a while (probably a decade or more) to finally convert. But even then, you will always have legacy parts that are in one or the other. I prefer the metric, and I keep a text file open while I am working that has mm to mils, in single mil increments, from 1 mil to about 20 mil, then in 10 mil increments to about 100 mil. For the most common sizes, you really start to remember the conversions, like 6 mil = 0.1524mm, 5 mil = 0.127mm, etc.
Those are the two I deal with mostly. I also note the power (current) capability of trace widths for when I'm routing power.
As for routing the 0.8mm pitch BGA, you can actually get away with a 0.1524mm (6 mil) trace between the pads, but the 0.127mm (5 mil) traces give you a little more room if you are doing a lot of traces or wide buses (i.e. memory interfaces and such). Some of the documentation specifies that you can get *two* 0.076mm (3 mil) traces between 0.8mm pitch pads! That is insane to me, but it will probably become the normal in a few years. I can certainly say it would have made my current PCB *much* easier to route! For now I try to stay at 0.1524mm (6 mil) or above, and only use 0.127mm (5 mil) when necessary, and I have not had any problems with the PCBs (all were done by OSHPark so far during my prototype stage).