well, its pretty safe if you have to correct equipment and you know what you are doing, although i guess its possible to get you ride screwed with this as well, but then again, as they say, not taking risks is risky, so, i think i should give it a try
there are various different softwares available on internet. or if there is some good api available, i think i should be able to write my own software.
btw, there is a very famous obd device called scangauge II http://www.scangauge.com/, but i don't think it would be available here in pakistan, if anyone have any idea, please let me know.
you can find some good reviews of this thing as well, if you google around a bit