I’m fine with in vitro conception, but not okay with just throwing away embryos when the parents decide they’re done having kids. There’s a lot of emotion involved in adoption, but I think it would be better to donate one’s leftover embryos rather than let them just sit there, doing nothing. I think I would have an easier time knowing that I gave all of my children a chance at being born, even if someone else is raising them, rather than knowing that some of them will never have a chance because they’re in a lab somewhere. Disclaimer: I have never been infertile so I am speculating as to what I’d do. Nobody knows until they’ve been in that situation.
Before I go on, I realize that a lot of times conception doesn’t even happen in the dish. You may have 10 eggs and only, say, 4 become fertilized. In that case since those other 6 were never fertilized, I’ve got no problem with throwing them away.
The chances of 1 embryo working in IVF is slim so I can see why they implant several at a time. That’s fine, but killing off some of them later on because all of them happened to work? No. You implant X number of embryos, you should accept the risk that you may have X number of kids at once. I can’t see intentionally creating, say, 7 children and then making 4 of them become sacrificial lambs for the sake of saving the other 3 just because doctors and parents refuse to show a little restraint. Then again, if you don’t abort you’re running the chance of all of them being born so early that they’re all disabled, which is terrible too. I still can’t see killing some of them for a “what if,” though.
Europe doesn’t have this problem because most countries there won’t allow an excessive number of embryos to be implanted into a woman all at once. It probably increases the number of attempts that have to be made before a couple ends up with a kid, but to me it’s better than creating, say, 20 embryos, implanting 10, Mom gets pregnant with 5 so they go in and kill 2 of them, meanwhile the other 10 are in the deep freezer, forever forgotten.
OTOH, these same countries have socialized medicine and thus there are no private insurance companies limiting couples to just one or two tries with IVF (correct me if I’m wrong, Eurodopers). Some couples here probably are forced to implant an excessive number all at once because they know this will be their only shot. 
As far as the soul question, I just don’t know. I do believe we get a soul at conception, but as far as what happens when an embryo is frozen, I don’t know. I don’t believe souls are recycled, so if an embryo is frozen and God knows that that embryo will never be implanted, I imagine the soul would just go on to heaven. If God knows that the embryo will be implanted, maybe He works it a bit differently.
I’m not Catholic but I do agree with yBeayf’s statement that we should err on the side of caution.
To answer nyctea scandiaca’s (very good) question, sometimes people miscarry and never even know it. In very early miscarriages, I imagine there wouldn’t really be anything to, well, bury. In a later miscarriage, though, I don’t think I could see myself holding a full-fledged funeral, but yes, I would have the baby buried in a cemetery.
If it were a really, really late miscarriage or stillbirth, then yeah, funeral too, a small one.
As far as why a funeral in some instances and not others, I can’t answer it because I don’t know.