I don't have issues boxing 2 toons on 1 computer, but I don't use WinEQ. just load 2 instances of EQ and minimize one of them. It is slow to swap back and forth between them, but I usually don't have to anyways so it's not an issue for me.
The only problems I have had while running this macro:
(1) 1 or more chars dieing in Lavastorm from "a swirling smoke". This hasn't been issue for me lately, as my chars are now high enough level to stand there getting beat on for the 1 or 2 minutes I need to be in lavastorm.
(2) 1 or more computers/EQ clients crashing, and losing key characters, or enough chars that I only have 2 left and can't get a new mission. Not really a fault of the macro, but there should probably be something that is counting failures on first waves and if there's like 3 in a row it should /end. (I say first wave so it wouldn't end on failures counted for not looting). also it should /end if the weary traveler says I don't have enough players in group. It currently just sits there spamming the halfling every 2 min making you look like an idiot if you don't have 3 in group.
(3) The mission ends prematuraly if you manually loot the gloves/earring, and anyone that hasn't looted a shard yet loses out. Not sure if this the macro or the mission. Easiest way around it is for the player to make sure everyone looted a shard before grabbing the loot.
(4) I had 1 mission incomplete because either not enough mobs spawned in a wave or the kill didn't count, and it sat there waiting, neither a failure (naggy didn't die) nor a win (had 95/96 mobs dead only). That happened only 1 time to me, but there probably should be some sort of timer and if a mission takes longer than an hour it should end the mission and try a new one instead of getting no xp for 6 hours.
Overall the macro is very good and the majority of the failures I've had are due to client/computer crashes or the mission itself bugging out and not the fault of the macro.