>>1
It is ok. It shows the code and data flow better and more concise than plain asm, which is mostly useful in big functions (kind of like the graph view but better). It won't make all reversing easier, but sometimes it helps a bit.
It can handle other languages pretty good; it's just C-ified asm. My ancient version (YAG release from last December) doesn't handle fastcall, but I'm sure that's fixed now.
>>3
Olly is good for debugging, but you can't beat IDA for deadlisting.
>>4
IDA's linux version.