I think it's funny when it works. My main criticism of your comics so far is that sometimes the punchline is too much of a non sequitur. I like Fianchetto for some reason, but I found Fustercluck pointless and flat.
Also, I like the first two panels of You Know What I Mean? a lot better than the last one. If your joke really only needs two panels, try using the "black" background to simulate a strip of that length. Or try using a pregnant pause in the middle panel, or stretching less dialogue over more space.
Opinions differ on that one. For the most part I try not to, in the interest of making each strip accessible to a random reader, but you're certainly in good company if you do it.
Comics are naturally a quick, often blunt medium. Unless you have a reason, I'd recommend saying as much as you can in as few words as possible.
Don't worry about whether it's been overdone, as long as you're doing it well. Like theburninator said, it may not always be possible due to the limited selection of characters. However, some of the different expressions that are available can be used to good effect. Maura's eyes-shut pose is practically a punchline in itself.
Practice and you'll get it. You're off to a good start. Welcome to Stripcreator.
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The what mentioned above is total fiction. Please don't take it seriously!