I'm ashamed to say that I'm one of those people who doesn't wash their makeup brushes enough. I use a brush sanitizer spray to keep them free of bacteria but I don't give them a full wash as often as I should.
It may be partly down to laziness but as I use them every day I actually find it difficult being able to wash and dry them before I need to use them again. I discovered the sigma dry n shape online quite some time ago but it's one of those items I never got around to buying so I was thrilled when my mum bought it for me for my birthday