If socks were good enough to take the time to knit in the first place, they're typically good enough to take the time to darn them to extend their life. I have two pairs of every-day wear socks, socks that are in sturdy enough yarn to not worry (much) about wear or machine washings, and not in work-specific colors. Both pairs are in need of patching so I can continue wearing them. I also should use some of that sock yarn I own...more socks are never a problem!
The first one was knit for me in a swap. The Monkey pattern, in, ummm...I forget. I looked through old blog entries to see what it was, and remembered that I wanted to make some Thelonius in black for work (I may just do that...), but couldn't find the yarn. I think it was Cherry Tree Hill, but it might have been Socks that Rock. One of those two big ones. I think CTH. Yes, found it in the comments, Cherry Tree Hill! Either way, I don't like it; it pills a lot and looks really old and washed-out. It's also knit a bit loosely for my tastes, and I'd considered ripping it out and re-knitting when I first got them, but am glad I didn't because I've worn them quite a bit and do enjoy them as-is. I noticed a split stitch in the heel awhile back, but never reinforced it. It broke, and just needed a simple 5-stitch graft using some gorgeous Indigo Moon, as it's the closest color I have. I again considered frogging to re-knit, but I have more than enough sock yarn now, and the yarn doesn't seem all that pretty anymore. Darning it is a lot faster and easier than ripping to re-knit!
I knit my socks fairly tightly, but not tight enough for Dream in Color Smooshy, apparently, and I managed to wear through both bottoms at the same time. It was a couple of years of near-weekly wear, so I'm not complaining much! I was thinking I should reinforce it (noticing a pattern?), because reinforcing is always better than darning a hole, but I never did. Instead of trying to darn a fairly large hole with quite a bit of open ends, I'm knitting patches on them. It's not that I couldn't darn them, but it would take awhile, and since I have to use a different yarn anyway, as long as the patches don't bother me while walking about in them, it's good to go.
Sock (or any other garment) patches, step 1:
Pick up stitches below the hole. The best way to do this is to pick up the rightmost leg of each stitch, so that the join is nice and flat. Depending on yarn size and how worn the yarn around the hole looks, pick up from at least two rows below the hole. I picked up stitches on the third row under the hole.
Step 2 (optional):
Because the yarn was so worn, I used some Fray-Check to help prevent further degradation of the original sock. If those ends unravel enough, the patch will fall off anyway, and that is undesirable.
Choose your yarn! I didn't have any leftovers, I'd sent them to a friend who was making a sock yarn blanket. I wanted a yarn that was similar to the yarn I was using in feel, thickness, and hopefully color palette, and definitely washability. I chose the yarn on the left.
Knit a patch. Knit across the row you've picked up, joining the yarn in whatever way suits you. You should be knitting one patch row for every sock row. Knit (or purl) the first and last stitch of every row with the one it's on top of on the sock, again picking up the rightmost leg of the stitches. You're joining the patch as you go, instead of making a patch and sewing it on afterward, making for a smoother join and less finishing, woo!
After you've knit a couple rows past the hole, graft the patch closed. Follow the stitches of the row above your patch to graft it to the next row, as if the graft were another row of stitches. It's really like duplicate stitching, except you're stitching into the live stitches.
Wear with pride, enjoying your sock for as long as possible before you absolutely must throw in the towel and throw away (or frog to re-use) your lovely socks.
I've worn them a few times now, and I was worried that I'd feel the patches and be unable to wear them. Of course, your mileage may vary, but for me, I feel them when I'm walking around the house in only the socks, but not when I'm wearing them with shoes or slippers. I'm happy with them!