MAF = Mass Air Flow

 

Few Hondas evenhave a MAF sensor. But he's in California. Possibly the ULEV engine does have one.

 

When did you last change the trans oil? I changed mine at about 70,000 miles and shifted much easier.

 

Like it was said before, try bleeding your clutch master cylinder (if air is in the line the clutch will not completely disengage to allow you to shift). Bleeding a clutch master cylinder is easier than bleeding brakes, same principle, I have done it in the Integra and the Legend and in a 626 and use only Honda fluid (brake fluid) to do this. If this does not help you may have a sticky clutch (requires replacement to fix).
As far as your gas mileage, my suggestion is to put what the owners manual suggested octane level in it. If it says minimum 88, (whicha lot ofI4's do), then put plus in it (utah plus is 89), don't put regular in it, it will cause your MPG to go down. A few dimes more at the pump could up your gas mileage substantually. I wouldn't be replacing any O2 sensors if the CEL is not on.
Probably a stupid question but, did you check your Air Filter?
Low tire pressure is a huge loss in MPG, if your not up to at least 31-35 PSIyour MPG will go way down.
Check your tire pressure, put decent gas in it, and see what happens.

 

Check this out ...
http://www.metacafe.com/watch/524517...as_mileage_2x/

 

Did not know that pure acetone could have a drastic effect...that would like a 10mpg jump! O_O

EDIT- This is darn cool. http://www.metacafe.com/watch/501379...ith_airduster/

 

I'm pretty sure I read somewhere that using acetone had more negative affects than posetive ones. I think it eats away at fuel pump parts and seals in your gas tank or something....I forget