I've been in lots of swaps, both here and elsewhere. There have been a few negative experiences, but the positive ones far outweigh the negatives.
For example, there have been some blocks I got back that were difficult or impossible to use, either blocks that were too small/large and had a design that made it impossible to make it resize without losing the pattern, or blocks that were poorly constructed and had such a tiny seam allowance (1/8" or less!) that they would've fallen apart during the first laundering. I resized/repaired what I could, but even so, a few blocks ended up in the scrap bin. Personally, I'd much rather have a correctly-sized, well-constructed simple 9-patch block than a fancy, but poorly-constructed, incorrectly-sized block. I can usually fudge about 1/8" - 3/16" on the size, but any more than that, and the block just doesn't want to play nicely.
And there were a couple of swaps where the hostess vanished. On one of them, after MANY letters and phone calls, the hostess finally reappeared long enough to mail everyone's blocks back, then she disappeared again after that. And on another swap, the hostess said there was a family emergency, but even after several months, nobody heard anything else from her. That one was a person-to-person swap, so nobody was out any blocks, but it was puzzling nonetheless. I still wonder about both of them, and hope they're okay.
I've been in the Boomerang swaps since #3, and there are almost always a couple of folks that never complete the blocks or return your F8. The blocks I have received, however, have been SUPER-nice, and make up for the missing ones. Just expect that a couple of people will probably not finish, for various reasons. (I do think their intentions are good, but things come up along the way ... illness, new job, etc.)
So, anyway, yeah, if you do a swap expecting absolute perfection, you'll likely be disappointed, but if you keep your mind open and do the swap for fun, you'll usually get back some blocks or fabrics that you actually love, but wouldn't have thought to make/buy yourself.
Swaps are also a good way to make new friends, and to see how other people do things, and learn from them.
I say go for it!
