If I'm running a combat and I have a player or two who are only getting one turn in a round while other players are getting 2 or 3, I feel bad, and it seems unfun/unfair that as players they get less screen time because they chose to play characters who aren't all souped up with reflex enhancements. Sure extra initiative passes may be a way of showing that certain characters are jacked up and really quick, but I don't think it is a fun one for players who want to play other types of characters. It's important to keep in mind that it is a game we are playing and players come to participate not to sit around and watch other players play the game, so to me it makes sense to find an alternative way to show that jacked up characters can be really quick and bad ass.
Fortunately, this hasn't yet been a huge issue with my Shadowrun game because there hasn't been much combat, and the fights that we have had have usually been completed in about 1-3 rounds.