I would recommend using color box found here: http://colorpowered.com/colorbox/ Thickbox was essentially a jQuery plugin proof of concept by Paul Irish that he has not maintained in years. Another option is to use the jQuery UI dialog box. jQuery UI is heavier but if you need any of the their other widgets like a datepicker or accordion might as well bite the bullet and go that direction.
The short answer is no, you do not need to include this.
HTML5 is a lot more liberal, the spec allows any combination of characters inside of a pair of script tags, but makes special exceptions for HTML comments "<!–", and "–>" and also the script tag pairs themselves, "<script>", and "</script>". So long as you're careful when including any of these substrings inside of a pair of script tags you do not need to worry about including comments/escape sequences within your script tags!
I think this explains it pretty well:
From "Christoph" on StackOverflow.
Closure Compiler (Closure Tools – Google Developers) enforces this rule while minifying, so if you're also looking for a minifier, it can be a good choice.
 Technically, I think JSHint has just been rewritten so that it is no longer dependent on the original JSLint code, but it started off as a fork and is of course still inspired by JSLint (and its inadequacies).
Is it possible you checked the height and width properties prior to the image being downloaded?
You can either wait for the image to completely load (you can set an onload handler to catch this event), or if you don't want to wait for potentially large images, you can do a setTimeout() and keep checking the image for a height and width property. I have used this approach quite reliably in all reasonable browsers back to IE6.
Projects like CoffeeScript, Objective J and GWT are an interesting new trend.
During the Google Wave presentation, they talked about how amazing GWT was, how it allowed them to think differently about what's possible in browsers. Google Wave is a terrible application, with constant script timeout errors and overall poor performance. That's not good, but the newest version of Google Documents might be coded with GWT, as well as other apps that are released and in wide use.
Google's Quake 2 Demo was ported from Java with the help of GWT.
If there is something serious to be afraid of, it's a lack of community around CoffeeScript, not enough projects using it, few libraries catered to it. So if we don't use it, we'll lose it.
No. I've verified with Chrome 12 and the profiler, there are no memory leaks after running your snippet. It should be said though that jQuery has it's own garbage collector, you might not get the same results adding your elements manually to the DOM.
Well, you kind of answered your own question – if you want to avoid callbacks, you can instead fire browser/custom events and catch + respond to them.