-- do not open up the two front holes and tape the third one as suggested by an old old post that I read. I tried this and while I got a lot more bass, the highs were so colorful and forward that it was quite painful to listen to cymbals in music.
-- for my second attempt, I only opened up the middle hole as how WJE suggested and left the two outer holes covered by the original mesh tape. This provided slightly less bass from my first bass mod attempt but the bass will still rock your pants. Seriously, I've never appreciated Far East Movement's "Like A G6" track before. If you want a percentage of how much bass you'll get, I'd say this mod gives about 40-50% more bass and that's not saying much. It improves the boom and does so to a good portion of the lower spectrum.
-- you must do the putty mod if you plan on opening the bass hole(s). As already stated by those who have done it, I will repeat them by saying that doing the putty mod really does tighten up the bass gained. Without this putty mod, the bass becomes really fuzzy and will leak into your mids. Your bassy music will sound really bad. I went to Walmart and picked up a pack of Loctite Adhesive tack in the office supplies section. It comes in a thin, palm-size pack that has 5 strips of the blue stuff. It sticks pretty well but only time will tell how long it will remain clinged to the surface of the driver. I used about 40% of one strip for each side as there's not enough room to apply a thick layer and I only applied as much as I felt was necessary. You probably won't want it thick anyways as it will make it very difficult to open it back up to make adjustments to your mod. The adhesive strength will hurt your fingernails. It did mine.
Still, I find it unbelievable how well this mod does to tighten up the bass from the bass mod.
Edit: here's a picture of the Loctite putty.
http://www.loctiteproducts.com/img/products/big/cntct_putty.png