I associate people with both their usernames and avis. So it does annoy me when people change their avis, coz when I glance at the side to see who wrote the post, I don't recognize the new one. Like kittenpoker, who I always associate with Buffy in a construction hat, or Chosen Enemy, who I picture as Buffy smiling in Chosen. I also assume that you're the gender that your avi is, lol. I think I wrote 'she' instead of 'he' for ILLYRIAN because he has Willow as his avi. And I love it when people don't change their avis, so I can always have the same impression of them in picture form. Like sosa lola, who will always be Xander.
tl;dr Don't change your avis!