Sorry if this is ridiculously noobie but I hope it’s at least a quickie: I know Applescript is an awesome tool to manipulate/send instructions between applications, but what about the applications themselves? Can one add, say, a programmable button to most Apple apps? Something like how some Windows apps allow custom macros. How trivial is it to customize an app?
Not trivial, and often not possible unless the application will accept plug-ins. I don’t know of any plug-ins written in AppleScript, but there may be some.
Control of an application is more basic than “inter-application” control.
You may not be able to create a “programmable button” in every app but you can put scripts in the Script Menu and run them from the menu for incredible power/efficiency. You can’t do EVERYTHING, but you can go miles beyond a Windows macro.
SC
Well, I dunno. I suspect it may depend on the complexity of the script/program in either case. And besides, I wasn’t trying to make some qualitative judgement about which kind of programming is inherently more sophisticated. I recognize that many languages have a natural balliwick in specific domains and may excel at that but not so much in other areas. Doesn’t mean that overall it’s crap. Examples are javascript, actionscript or even php. 
So in the same light I was only wondering if I could use AppleScript to (easily) customize existing programs (like, say, Excel or Mail), y’know, beyond it’s acknowledged supremacy in inter-app/system automation.
Mebbe it’s my bad for using “macro” as it does have different connotations. Macros in Lisp, for example, is a completely different thing from the idea of simply recording keystrokes and clicks. Even in Windows, macros can be taken a couple of different ways. I was thinking of macro-as-script (aka vba), which can be used to (f’rinstance) stick in an extra button (or extra menu option or keyboard shortcut or whatever) with customized functionality in the menu bar.
Anyway. I don’t want anyone to get the idea I’m trolling on M$'s behalf. I am not. My wife has had a Mac for a couple of years, but I’ve pretty much ignored it, sticking to the devil I knew (ok and mostly cuz she doesn’t let me touch it :P). I think I’m ready to switch and make a committment to Mac as my main platform for computer tomfoolery, but I just wanted to iron out a few potential nits (and understand and be comfortable with the workarounds).
At any rate, thanks for pointing me to the Script Menu. I’ve found a few articles that discuss this feature. Yes, this, I think, will do quite nicely 
Trust me, you won’t regret this.