1) is caused by a new feature that should help swarming. As a negative side effect it makes downloading from clients with buggy http11 support (this seems to include LimeWire) almost impossible.

2) Maybe you could post the error message here, so I could tell you what's causing it.

3) It's been a problem for ages and it's caused by illegal characters in the file name. A way to fix this (at least partially) is to add '\' , ';' and whatever characters your OS doesn't like to the ignored keywords list in the options.

4) I don't see slower downloads in general. However download reliability is reduced because of 1)