Okay, so lots of people commenting on the previous post (and in email) wanted to know how to choose a sewing machine. Or what model they should buy, specifically. I can't tell you what model to buy … in the same way I couldn't tell you what kind of car to buy, or what flavor of Life Savers you should like. You have to choose one that fits YOU. (Scary, I know.)
First off, remember that most of the choices ahead of you are good. Your life will not be ruined if you buy the "wrong" machine. No one will mock or scorn you for not optimizing your purchase to the utmost. Remember that the perfect is the enemy of the good, and with sewing machines (and with other things like digital cameras and so forth) the more time you spend reading about them the more high-end features will seem like necessities … and so your "dream machine" will get more and more expensive (and further and further out of reach).
These instructions are predicated on my assumption that you don't have a lot of money to spend on a machine. If you just won the lottery, have a rich uncle, or are independently wealthy, just buy whatever you see first. If it turns out wrong you can just go buy another one.
So. To buy a sewing machine, first you need to figure out whether you are an experienced machine user or not. If you have never used a sewing machine, then that answers the question: you are not. In that case, WHAT machine you buy is a lot less important than WHERE you buy it. You want to buy locally, from someone who offers classes, and who will guarantee the machine and offers a good warranty for repairs. (The exception to this rule: if you want to buy a machine from a friend who is upgrading her machine and promises she will teach you how to use it … and you believe her … go ahead and do it. Otherwise, buy from a local shop.)
Go to your local shop (if you're lucky enough to have one!) and tell 'em right off you're not buying that day, only looking. If you are a complete novice, tell them that. Ask to try out some machines. Better yet, if some place near you offers sewing classes, take one before even thinking about buying your own machine. You'll get comfortable with the classroom machine and will know what you like and dislike about it, and then you'll be able to articulate what you want in your own machine (automatic threading, a knee lift, whatever). Take notes. Tell them what you sew (dresses? handbags? quilts? fabric art? Someone who alters a lot of jeans needs a sturdier machine than someone who makes organza wall hangings, for instance.), ask for recommendations, try things out, write down model numbers, and tell them you'll be back. Ask if there are things that people usually ask that you're not asking. (This is a good question for buying just about anything. You'd be surprised how many people selling things don't answer the questions you should be asking. "Most people who come in to buy a howitzer ask about the kick. This one has quite a bit of a kick … this one over here is a little softer.")
If you're new to sewing, definitely try for a used machine from your local shop. Ask about their trade-in policy. Most shops will be happy (or SHOULD BE HAPPY) to sell you something a bit simpler and then have you trade it for something fancier later, rather than sell you something so intricate you'll never use it and never come back.
If you are an intermediate-level machine user (you've taken a couple of classes, made some skirts or tote bags), you probably know roughly what you like in a machine, and I recommend buying a used machine that was higher-end when it was new. Something with a good straight stitch and a good zigzag and maybe a buttonhole function, but not a lot of fancy embroidery stitches (unless embroidery stitches are your reason for sewing). Again, trying things out at a local shop is a good idea for you. You can also do the whole Craigslist/PennySaver/estate sale thing, too, if there's a good local repair shop you trust, because the price of a used machine plus a tuneup (my tuneups usually run $80) is cheap enough to be worth it. (Try to see if someone selling you a used machine will let you bring it back to them if the repair shop says it's not repairable. An estate sale won't let you do this, and if the machine is under $100 probably a Craigslist seller won't either. If the machine turns on and runs it is probably tune-uppable. If it won't run at all, makes horrible grinding noises, or smokes … not so much. Also, don't buy something that seems to be missing a lot of parts.) If you buy this kind of machine, you'll know when you've outgrown it — you'll start wanting to make things that need special presser feet or you'll start being picky about the quality of your topstitching. Then you can upgrade.