I can click by putting light pressure but not actually "clicking" the trackpad. It's causing some weird things to happen.
I set mine as yours - TAP, but works both ways. Tap or Hard Click.
my 2001 mba was acting strange when moving around the cursor sometimes even highlighted lines and the whole page. I called service many times , reinstalled lion 2x before apple told me i had a defective trackpad and to take it into an authorized service center which is not so common in hcm vietnam. 1 week later i got my air back and seems to work for now.
So yes a defective trackpad can happen.
2001? Mba?
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OP, why don't take a look to a MBA (or, for the case is the same, a MBP) in some store? And simply check against yours. Check the pressure you have to apply and the clicking feel.
Have a close look at yours. Check for some minimum obtrusion you can have, for instance a piece of cookie, etc. Eventually use a bottle of compressed air all way around. I got something removed from underneath my keyboard that way. I used to borrow my kids my laptop...