WHY NOT TO UPGRADE YOUR MAF
Many people think they need to upgrade their MAF. The truth is you dont need a new MAF until the stock one is pegged. Its not so much as to what amount of hp will peg one, but the amount of air going through it. But as a rule of thumb, we will go with 400rwhp. Now Im not saying go out and buy a new one if you're at 400rwhp, you need to datalog the MAF counts and such to see if you need a new one. VERY rarely will someone with a NA car peg the stock MAF.
What does upgrading to a larger MAF do?
Basically it will lean you out and cause the car to run very poorly. As a result you will need to get the car retuned. If you dont, then the lean condition your new MAF causes will lead to a blown motor. Now after you get the new MAF and have the car retuned the gains are very minimal. So that makes your new MAF pointless.
Also, just as a side note, intakes with a bend before the MAF cause bad readings. So stay away from those too.
It gets into more detail here. And for those who dont know who Ed Clark is, he is a VERY reputable tuner at Steen Racing. http://forums.modulardepot.com/showthread.php?t=25092