I have a microphone but cant always use it as I have a baby that I would wake. But I disagree that you NEED a microphone to play. You can easily see that your team mates are getting eaten without the need for a microphone by simply looking around.
While mics are not essential, they offer a great advantage; Sure, you can see you teammates - most of the time, but what about when the horde descends and you lose them in the chaos.
Besides, mics are indespensible for...
What does annoy me is when you get idiots on mics that bark orders and think they are great, yelling out insults when you arent helping them, even if you are not able to at that moment.
...
planning and co-ordinating with teammates. I'm generally quite vocal, even when playing with strangers. Some people don't like taking orders (even though though they are usually 'suggestions' rather than orders) but for some reason, these people usually tend to be the onese without mics. People with mics tend to take 'orders' better, presumably because they can issue their own or counter them, and they appreciate the teamwork benefits they bring.
There is a big advantage if a) the team have mics and b) one person leads (it can be different people over different parts of the map, of course). Having someone verbalising plans, and suggesting the next move is a great help. I do it a lot, but I'm more than happy to follow; in fact sometimes I suggest player x takes the lead (often because I'm lagging behind or am walking wounded). I've saved our bacon plenty of times, and I've arsed it up plenty too, and have been over-ruled on a daily basis. But if all 4 members follow the same plan and move as one unit, you can make a sub-optimal choice (like going the wrong way or waiting too long in one place) and still survive. I'm almost certain that I've wound some of my teammates up on occasion, but they keep wanting to play with me, so I assume I must be doing some thing right (Meddle is probably going to put me right on this one, now!

)
Without mics, you have ridiculous moments where you are trying to type in requests, offer suggestions, plan the next move -all while trying not to get raped by a hunter. You have to look around to see where your teammates are all the time. You have to spot when they are healing or reloading (on mic I'll say 'healing', or 'you guys heal, I'll cover'). You tend to stumble along the beaten path because you can't easily communicate a radical change of plan or articulate a new tactic. You can't easily congratulate the sterling work of a teammate, nor 'vote' on what to do next. And you can easily be misconstrued via text, but less-so via talk.
However, I understand about your baby. I've woken up my daughter shouting 'Ahhhh....Get that ******* hunter off my back!' on the odd occasion.
Then I normally surprise them by coming on mic and they shut up. All mouth until they realise that you can talk back.
I never insult anyone or rant and rave, but people disagree with suggestions all the time. It's no big deal. I tend to have the comfort of playing with one or more friends, so anyone causing genuine aggro is immediately isolated (if not voted off), but to be fair, although I frequently complain about teammates who go off on their own, I haven't found there to be that much of a problem with players abusing others. There are are the odd guys who TK (presumably to become Infected quicker) and there are others who insult 'inferior' teammates, but not many, and they are soon removed. Genuine team payers are drawn to this game and they tend to fare better than the rambo types.
Meh.
Oh, those *insert race/culture here*, they always *insert stereotypical behaviour here*. Ho ho ho.
Tedious.
Quite.
Apart from the language barrier, I've enjoyed plenty of good games with players from all over Europe. In fact, I'm often surprised at how well some can communicate in English (under duress); which is more than could be said about many of my countrymen.