For the sake of the question, this includes all forms of initiative enhancement (cyber, bio, magical, etc.) that increases initiative passes. How common or prevalent are they in stories and games? Are they specialized gear that is actually special or is it something necessary for a good runner's survival? It is something more exclusive to elite security forces (Red Samurai, Ghosts, etc.) or does everyone have it in some form?
The reason behind the question is for character background and trying to get a general understanding of the power levels between augmented and norms.
For a good exploration of what it means to have a group of 'normals' - such as gang members - be augmented even so simply as one level of wired reflexes, look into Mary K. Kuhner's Shadowrun-based fiction, "
Jayhawk".
In regards to prevalence, though, you should look at what it takes on its most basic level to gain: cost.
A smartlink (your first necessary cyber-based combat purchase) is 1,000¥. That is 50% of the monthly cost for a low lifestyle - 20% for a middle.
Wired-1, on the other hand, is 11,000¥: more than double what an ordinary white-collar citizen is going to make in a month. it's almost six months' pay for a blue-collar worker -
pay, not 'what's left over'. If you think of it investment-wise, and if a citizen has 10% left over after lifestyle costs, at 500¥/mo this is almost two year's savings for a white-collar (middle-lifestyle) worker - or over
nine years worth for the blue-collar worker who has only an extra 100¥ per month. From a corporate standpoint, it is an
investment in your future -- and you can believe that they're going to make damn sure they get their money's worth.
In Jayhawk - even before the very beginning of the story - Kuhner's GM wondered what it would be like to have an entire gang (15-30 people) with wired reflexes, how that would affect combat, etc. And only afterwards did they get into what that would mean financially (330,000¥ investment just for that), and what the corporation who did it would
want with such a group, etc. etc.
Overall, you'll find maybe one in a hundred, one in a hundred fifty people in a crowd with some sort of reflex boost. In a group of specialists, e.g. security guards or cops, that ratio will increase immensely, so that you're talking about 1 in 10 or 15. Shadowrunners? 2 out of 3, if not 9 in 10,
somehow - and almost always in their area of expertise, i.e. the hacker may not have physical reflex enhancements, but you can be sure his commlink is juiced.