According to my profile page, I've been here since December of 2010. As for how much I've improved? I have no idea(though I would hope I've only improved). I took leave of osu! around 2012, then only stopped in every blue moon to see what was happening.
I've only just recently started playing maps with the intent to actually improve. Back when I first started I would only play the approved beatmaps with the occasional map I could actually pass thrown in so I never got better at the game, then eventually I just gave up. Plus my hard-drive crashed around the same time, losing all my stuff as well as windows, so I didn't really bother seriously trying to come back for the longest time.