Word verification

A few readers have mentioned they've had problems with word verifications on comments they try to send to the blog. You need to type a couple of words which are shown in distorted type. I've had similar problems on other sites.
Word verification is supposed to protect me from receiving a whole load of spam comments. I already get quite a few, often people wanting to post a comment with a link to their non-relevant website.
As an experiment I'm turning off word verification, but will quickly turn it on again if the spam load becomes excessive.