Is there a way to speed up my boot to about 15-20 sec? This is my current boot. I already enabled concurrency in /etc/init.d/rc and disabled some useless daemons. Would compiling a custom kernel shave off a lot? I also read somewhere a while back that compiling drivers directly into the kernel speeds things up. I have no idea how that would work, especially with nvidia's driver.

Any tips appreciated

there are a great many things in the boot scripts that have timeouts, like "sleep 5s". if you spend a lot of time going through the scripts, and finding the minimum amount of time your machine needs for things, you can shave many seconds off of your boot time.

Best way to speed it up is compile a custom kernel and make sure that you rip out all that is not strictly needed. As for the benefit of compiling everything into the kernel, I don't know. Modules load and unload so fast that it won't make much of a difference IMHO. Of course, some HAVE to be compiled in but only because your system won't boot properly if you don't.
That being said, I recently compiled a custom kernel on my Ubuntu system. It took nearly two hours to go over all the options and to do the compilation. The net result is that my system now boots ten seconds faster. Two hours - ten seconds. You tell me how many times I'll need to boot my system to compensate for the two hours I invested. By the time I reach a break-even, I'll have moved to a different kernel if not a new system. Still, compiling a kernel is an experience in its own right that can be quite interesting so I'm obviously not telling you that it's not a good idea.