in the early days i changed my domain itilskeptic.org to itskeptic.org. Dumb thing to do but the blog was still low profile and i got through it. i kept itilskeptic.org live with an auto-forward to the new domain. After a couple of years i saw i was getting very few incoming traffic with itilskeptic.org as the referrer, so when it came up for renewal i let it expire.
Google page rank dropped from 5 to 4.
Why? Even though few people were coming that way i still had some nice respectable sites pointing to itilskeptic.org and i lost all the "linky love".
keep those old domains that redirect!!!