Is it acceptable, or advisable, to include self-assessed ratings of your skills on your CV
What scale do you intend to rate yourself on?  Maybe that sounds like a silly riposte, but that's a serious issue.  If you say you're proficient in Java, how does the person reading the CV know what on earth you mean (assuming they're willing to take your word for it).  I would be much more inclined to focus on what experience you have with a language (I have X many years of Java programming experience, I've done such and such projects), since that's actually something which people understand the meaning of.  You also don't necessarily need to cover this in a lot of detail in your CV, since if you're applying for a job where these skills are relevant, you can mention it in your cover letter.

EDIT: In response to the proposal of using stars or a 0-5 rating:  DON'T DO IT!  If you want to write "I'm proficient in Java and have some experience in C" that's harmless but won't make too much of a positive impression either without some more concrete information.  The stars will make you look eccentric at best, and lunatic at worst.  I know that some times the usual convention about how to do things seem constraining and silly, but if you've never seen something on a CV before (and I've never seen giving yourself numerical ratings on an unknown scale), there's probably a good reason.