I have insurance from my employer now, there is a downside to everything so what bad will come of this if it passes for me and everyone else that already has health insurance from their employers?
First, it already passed. There are additional changes that may or may not pass, but the basic structure is now there.
Generally speaking, if you already have insurance, there are no direct changes, unless you have one of the so-called "Cadillac plans", which are super-expensive plans that provide little additional benefit compared to their increased cost. Unless you're part of a labor union, you probably don't have one. If you do, though, there is a tax on the cost of the plan over a set amount.
Indirectly, there will probably be a transition period where wait times for services may be longer, as the infrastructure comes to grips with a massive influx of people who suddenly have insurance. It's not as if all 23 million people get coverage at once, though. Only those who have preexisting conditions will be affected now. The rest will become covered in 2013.
I can't think of anything else that might have a more-or-less "soon" negative repercussion.