Here is the second part of my little tutorial, this is how I've dealt with the holes left on the thumbs of mittens when you pick up the stitches (this is the thumb gusset version of a mitten).
So, when you start your thumb you will want to leave a fairly long tail so you will be able to do this. It's basically a duplicate stitch over the open space.
Thread the tail end of the yarn from the thumb through a tapestry needle. Starting with the needle/yarn on the inside of the mitten, pull the needle through the space under the last "ladder leg" before the hole. (If you pull columns of stitches apart the yarn in between looks like a ladder)
Skipping the row above where you just brought your needle through (you'll notice that the stitches directly above are a little loose) go under the left leg of the stitch on the right and the right leg of the stitch on the left, pull through.
Finally go back through the space that you came out of originally and pull through.
Ta da! You created a stitch to fill the space.
Weave over to the other side of the thumb and repeat (I usually just go through a couple of the purl bumps to get to where I'm going so there's not a float there).
I hope this is clear! Please let me know if you have any questions.
Also note that this isn't really a seamless solution, however if you are making the mittens for a nonknitting friend or if you don't mind it, it's a good solution. I'm sure with a little finagling you could get it to look more seamless.
Incidentally these mittens are for a nonknitter, my step dad. I'm certain he won't notice anything out of place. I started these on Saturday and I finished the first on Sunday. I have the cuff and most of the gusset knitted on the 2nd, although I did most of that yesterday. Today I was playing some Mario Galaxy. I got a hankering for some Mario after playing Mario Party at a friend's house on Sunday.
I also finished a pair of fingerless mitts for my little brother. I have yet to take photos because they were blocking Saturday night and Sunday I was out. The sun is setting close to 5:30p and I don't get off of work until 5 so there's not a lot of daylight for photos. They will have to wait until the weekend.