I've done A LOT of garment sewing and have never had any major problems with grain. The main reason for this is PRE-WASHING and drying, before cutting. With the initial wash/dry, most fabrics will fall into their natural shape, which usually makes the cut ends totally uneven, sometimes as much as a few inches, on each end! :-(

Like Neesie I made garments before I started quilting. I always pre-wash and dry my fabrics before using them and have had very little trouble lining up the grain. If I have a doubt I will pull one thread to make sure it is lined right.

One of the problem I see new quilters have .. is they try to use the manufactures fold to guide the folding before cutting. Often this leads to the dreaded V or W cut in the fabric. If you don't prewash its important to at least ress out the bolt fold and restablish the fold going selvege to selvage or the dreaded V will most likely be an issue.
I do know a few quilters the dreaded V is something they just can't over come so they cut all their fabric into smaller units so they can cut without having to fold.
Getting the straight of grain is so important in cutting strips.
Tearing is always my first step before cutting. I used to pull threads.. now I am just to impatient for that method.

Still old fashioned and pull one thread. Lori is so right in saying that the manufacturer's fold, even with higher quality fabric, is seldom on grain, which is one more good reason to prewash and re-iron. Often the selvedges don't even match.

My Mom was the best seamstress I have ever seen...she would make a very slight cut in the edge of the fabric, carefully separate out one thread, and cut along that thread over the width of the fabric. Her seams were always as straight as an arrow and her quilts were lovely as well. So I'm guessing that her way (as usual!) WAS the best way...at least I can't argue with success. And no, I don't do it that way unless I'm making an heirloom quilt!

I have done this all too often, as 90% of my quilts are heirloom. Nothing irks me more than receiving expensive fabric ordered only to find the fabric was cut all wrong. Local retailers are infamous for this here. My LQS can be almost perfect to the nth of an inch. Frustrating to make a slit, cut along the thread (I cannot pull threads for the life of me) line to find that one end selvedge to selvedge is 3-4" longer than the other end. So, I also line up the patterns if there is one. To me it makes sense the printed pattern lines up. I find an exact pattern along the edge that I can use as a guide, then I straight cut along all 4 sides lining up the pattern, match up the pattern from front to back after folding, hold it up and move a smidgeon to create a straight fold. This I do after washing. Then I iron the fabric. Works for me.