Regarding Texas, it is NOT okay to shoot someone on your property in daylight. For the very reasons mentioned; there are instances where people could legitimately be on your property without prior approval, such as meter readers. At night however, the story changes.
Also, it is acceptable in Texas to defend your property as well as your safety. If a bad guy is trying to steal your car, you are within your rights to use deadly force to stop it. I think a guy shot a repo man a few years back, and after some legal wrangling he was not charged.
A carry permit is not as easy to get as it used to be, but it's still pretty easy (so I've heard). However there are plenty of exceptions to allow folks to legally keep a firearm handy, such as in a vehicle when you're crossing a county line. Which is admittedly a crock; I have property in another county, so all I have to do is say I was coming back from the farm.
One of my business partners went to New Orleans shortly after Katrina to do reconstruction work, and I loaned him my .357. For the first month he carried it on his hip, and never got a second glance from anyone including the police. Common sense sometimes does prevail. Fortunately he never had to use it, but I'm sure it served as a deterrent to the scumbags who were running rampant at the time.
I've also heard that if you DO have a carry permit, and do not come to the aid of someone being assaulted, you can be held liable. Like I said, just a rumor, but it makes sense to me; if you want the authority (to carry), you've gotta accept the responsibility (to protect).
As I understand it, the training classes required to get a carry permit emphasize when NOT to shoot; if you don't exhaust all other possibilities first, you are gonna be in deep yoghurt. Even if you are completely justified, and ultimately no-billed, you're likely still gonna spend a night or two at the Graybar Hotel; make sure it's worth it.
Oh yeah; when the cops DO show up, if you're still holding your weapon, put it down and step away from it. Cops are trained to immediately secure a 'monopoly on violence', and anyone not in uniform automatically constitutes a threat. Don't drop it like in the movies; good way to cause a discharge or bash up your expensive gun.
Peace Y'all,
c.