I tend to keep to one at a time, particularly for RP. I'm not very skilled at juggling more than that in all truth. 
I've played GW2, SWTOR, LoTRO, Planetside 2, Raiderz, and Tera - though the latter two were only for a few levels before I realized they weren't for me. There were a couple others here and there, but very few I got past the first level for. If I'm going to play an MMO till level cap, I have to commit to it. I can't MMO hop between two or more at a time depending on my mood that particular day, as shown by my transition from SWTOR to LoTRO. Which means that if I'm still playing FF14 by the time Star Citizen is released it'll be very interesting to see how I manage.
I've played GW2, SWTOR, LoTRO, Planetside 2, Raiderz, and Tera - though the latter two were only for a few levels before I realized they weren't for me. There were a couple others here and there, but very few I got past the first level for. If I'm going to play an MMO till level cap, I have to commit to it. I can't MMO hop between two or more at a time depending on my mood that particular day, as shown by my transition from SWTOR to LoTRO. Which means that if I'm still playing FF14 by the time Star Citizen is released it'll be very interesting to see how I manage.
