It does depend on who you are following because the people you're following show up when other people follow them---and a link is provided to let that person follow you. You can delete people who are following you pretty easy right inside Twitter. And you can set up a filter in your email to send those kinds of emails to the trash or another folder. Don't give up on Twitter because Google crawls Twitter constantly. I always Tweet my blog posts and I've noticed that the Tweet will show up on search results very quickly. Meaning my URL is out there fast. Especially if the person searches in 'real time'.
I do not feel it is spam . You need hard work to increase your followers, and then you will realise it.
in my opinion twitter is really full of spam.lots of people trying to promote their stuff.doesn't get any results either