I have always wondered this... If what i read is or is not porn, but i agree with the person that said that a story that has a plot and shows some sex scenes isn't really porn, but in the end it all depends, i believe if someone who's not familiar with this(mangas/yaoi/yuri) saw what i was reading, would with no doubt think i was looking at porn.. But since i know about the subject more than those who are not familiar with it and i don't read pointless feelingless mangas with "just sex",Then i don't think i'm in the wrong to believe is not porn...
But that also implies that there are mangas with just sex scenes and barely any plot in it, that i do consider porn. ** So... It depends on the manga, right? More than calling all yaois or yuris >porn<. **

** "It's so warm that, Before the snow has a chance to stick, He melts it for me." **