I'm in the process of switching factions right now to join a clan. I'm going from Tangent to Biotech and these two factions are enemies with each other. Since I couldn't get inside the Biotech HQ without the guards murdering me, I had to do 40 kill missions. (Did I miss something, was there another way??)
Having radiated roaches next to roaches, sewer flies next to sewer bees, etc, makes the process of finding the exact type of mob more boring and time consuming than it needs to be. I've seen some archived posts suggesting that kill missions be more general and I couldn't agree more. I'm suggesting something like "kill 10 creatures living in the sewers" or even "kill 5 enemies with a rank greater than 15."
Back in the day, you could get faction rep from killing other runners (and even some npcs). I suppose just gen-rep camping a noob alt to get your reputation up was pretty broken and silly, but you know what? it was a million times more interesting and fun than doing 40 sewer/cellar missions. I remember being afraid to kill another member of my own faction for fear of the reputation consequences; it actually affected player politics on some levels.
You could become factionless by ruining your faction reputation. Is it even possible to lose faction reputation today? I can't figure out how to lower my rep at all. I kinda wanna make another factionless, neg-SL, crazy guy that looks like an npc....