The only tiny issue I ever noticed with Notepad++ is that on some operations it switches from Windows to Unix line break style (CR+LF to just LF). That again only became relevant with encoding for some japanese characters. But Notepad++ is doing that during editing, so you see it when it happens and can switch it back.
Apart from that Notepad++ is the most complete free text editor I have ever used. Quite useful is also the "check xml syntax" option and the possibility to collapse/expand xml nodes, making navigation easier.
The UTF-8 implementation is very stable, which made me switch to Notepad++ in the first place, because windows notepad has some issues (most recently see
here). So yes, Notepad++ is highly recommended to be your only text editor. I DO NOT recommend to use windows notepad!