I never use "xxx" to sign off from messages to anyone, whether it be IRL or online. I usually use "<3" or ":)".
I think at first I thought I was too cool for all those x's when I was in junior high school when everyone else was doing it, and then as I grew older (and spent more time on the internet xD), I got more used to using "<3". I have no problems getting messages with "xxx" though ;)
I have used "xxx" ONCE - I remember it clearly: I was texting mum after something personal happened but she has no clue what "<3" meant so the only way I could convey my love was through "xxx". And that is all.
(typing all those "xxx" just then felt extremely weird tbh - I mean, my fourth finger on my LH almost never goes down to the x's, let alone consecutively..)