Any anti-spam measure that isn't something like a honeypot or security question is going to need user tracking. How else is it supposed to detect bots? Besides a plugin and not activated by default I don't see what you want them to do.
The option is don't enable the plugin...
Askismet can't do it's job without tracking so it's going to track if you want to use it.
Edit: And, users should assume info is being logged unless otherwise stated. I mean unless you set up your server yourself I guarantee there is a log created with their ip everytime they visit a page on your site.
If they are using IMAP instead of POP3 the emails themselves are like a log since they stay on the server until deleted. Same if you only use the web-based interface they provide.