First time mac owner, several beginner's questions

I just booted up my first mac (polycarbonate unibody macbook) and was instantly mesmerized by the look of the operating system. However, as I tinkered here and there, I've bumped into several problems.
1. When I edit a photo in iPhoto, how do I reverse the changes I made?
2. For iPhoto, when I imported my photos from my portable hard drive, where are the photo files saved? I can only see them via iPhoto, but I can't see them via some kind of file manager.
3. The face recognition feature doesn't seem to be working in iPhoto. I tagged a person's face in one photo, several dozens photos featuring the same person were never picked up.
3. Every time when I install a new application, the system always asks me to input administrator's password. How do I disable that? This is like having vista asking me cancel or allow on every action.
4. For firefox in windows, two finger tap on a link opens up the link in a new tab. But the mac two finger tap opens up the secondary menu. Is there a short cut for opening in tab for mac?
5. In finder, left column under places, there was an icon with the user name, when clicked, it displays folders for image, music, document, and etc. I wanted to drag that onto the doc, but it puffed into a smoke. Now how do I restore that shortcut?
6. How do I enable log in password? I can't find it in System Preferences>Accounts
7. The speaker hisses a lot, is this problem common among macbooks?
8. The plastic shell is so fragile. I dropped my flashdrive onto the cover and the usb tip made a dent. I was wearing my watch when I first typed on the macbook and bunch of hairline scratches immediately emerged. Are there any dent/scratch removal products out there?

1. Control-click the image and choose Revert to Original.
2. They're somewhat hidden inside the iPhoto Library file in your Pictures folder. You can view them by Control-clicking the file and choosing Show Package Contents. However, you generally should not touch the files inside or you can ruin your library. To work with files outside iPhoto, just drag the picture from iPhoto to the Desktop to make a copy and work with that. Otherwise, you can initiate most tasks from within iPhoto.
3. Try tagging that person in a few more for iPhoto to "learn" what the person looks like. Then click the Faces section in the sidebar and click that person's name. It should a section saying that the person "may also be in the photos below."
3(2). This depends on the installer. Some applications simply require that you type your password for technical reasons. It's not a somewhat false sense of security like Vista had. Other than during installations, you should not be asked for your password (unless you choose to lock preferences or something similar).
4. You can hold the Command key and click on the link to open it in a new tab.
5. Click the Finder icon in the Dock and it should open a new window displaying what is called your Home folder. Simply click the house icon at the top of the window and drag that to the sidebar (and/or the Dock).
6. In the Accounts System Preferences section, click the Login Options section in the left pane. For the Automatic login setting, choose Off.
7. I'm not familiar with that problem. Exactly when does it hiss? Just randomly?
8. I've never used it, but I've heard raving about this product. I think I even remember hearing that Geniuses at the Apple Store sometimes use it when you take in your Mac, though I can't verify that.

Hope that helps. Welcome to the community. (Oh, and in case you aren't yet aware, control-click is synonymous with right-click. Not everyone has right-clicking set up, particularly on the laptops, so it's better to refer to it as control-clicking.)

Thank you so much for your comprehensive answers!!! All of the solutions you provided have been very helpful.
As for question number 7, by hiss I mean pretty much constant hissing. When I'm watching a youtube video, whenever a person talks, his voice is accompanied by a hissing sound, like a zzzzz zzzzzz zzzzzz sound. This is kind of like putting an aluminum foil or something light but rigid over a normal speaker. Hope that gives you an idea of what I am trying to describe.

As for your question 2, you can right-click on the photo and select "Show File" (I think, it may be a different term). A finder window will open, displaying the image. What I often do then is to drag it to Photoshop (assuming you want to work on the photo) and immediately do a "save as...", rename it and save it to another location. However the changes will of course not be reflected in your iPhoto version of the image. So this may not be much help!

I suppose you could work on the iPhoto library image, just don't change the size or anything, and leave it a jpeg. then your new image will show your changes. But I wouldn't recommend this for any important photos.