Wow, this was a busy thread the last few days! It took me a while to get caught up.
The guy mistakenly arrested and turned over to ICE was an unfortunate incident. If I'm not mistaken, the Arizona law hasn't even gone into effect yet, so I think someone may have jumped the gun.
Immigration Officers don't need probable cause to stop someone and determine alienage. The Arizona law will not require probable cause either. It will require reasonable suspicion, which is a lower standard. The Arizona law mirrors federal law, but authorizes state and local police to challenge citizenship on someone they have stopped for other reasons and reasonably suspect that they are not in the country legally.
For those that think the law will be overturned, because immigration is in the purview of the federal government, remember that the FBI investigates bank robberies. So does local and state law enforcement. Local cops don't ignore bank robberies as a federal issue, because there are state laws that make robbing banks a state crime in addition to a federal crime. The other thing to remember is that local law enforcement is already authorized to enforce immigration law under section 287g of the Immigration & Nationality Act, as amended. What the state did in passing the law, was prevent local city councils from setting up "Sanctuary Cities" within the state.
As you can imagine, I disagree with giving legal status to illegal immigrants. That is rewarding criminal conduct. You don't let a bank robber keep the money he stole from the bank, so why would you give legal status to someone who entered the country illegally, except for political expedience? We might not be able to deport everyone who is here illegally, but we sure haven't tried yet!
What I would do, though, is allow people to apply for temporary work visas, so that they can legally live and work in the United States, but have no path to citizenship. Every year or two, they have to return to their home countries and apply for new work visas. If anyone was convicted of ANY crime (felony or misdemeanor) while they are here, they are deported and are NEVER given another visa of any type to return. NO CHAIN MIGRATION EITHER! If you fall in love with a foreign born person and want to marry and immigrate that person here, that's great, but no other family members, except maybe for under age children of the potential spouse. No mom, dad, brother, sister, cousin, uncle, aunt, grandma, grandpa, etc.
There is much I would like to change with the current law. For example, I would change the law with respect to "knowingly" hiring illegal immigrants by taking out the word knowingly from the law. I have to pay my share of the tax burden. I am held responsible for my tax form, even if I have someone else prepare it for me. The same should be true for hiring illegal immigrants. Businesses should be held accountable for hiring illegal immigrants. Period. They should be required to use e-verify and/or hire an expert to determine citizenship of job applicants. If they hire someone here illegally, they should pay a fine and/or go to jail. THAT will almost guarantee no illegal immigrants are hired, especially if it is enforced!
Another problem with the removal system is overcrowding of our detention facilities. Immigration Judges take WAY too long to hear removal cases. Federal judges in the District courts in many districts refuse to issue orders of removal on people who commit aggravated felonies and are prosecuted federally, even though they have the authority to do so under the law. As a result, we fill up bed space with people that could have been ordered removed as part of their federal criminal sentence.
I could go on, but it's time for some Jack Daniels!

Later!