We will not approve membership if the account name looks like a advertisement, is a e-mail address, or just sounds phoney, It is definitely better if a account name has some recognizable link to photography.
This is way too subjective and what may be an advertisement / email / phoney to you may just be perfect for someone else. Compound this by the fact that the username will be rejected after one day I doubt a genuine user who is rejected will bother to try again (I certainly wouldn't, but that's just me).
IMHO a captcha is a better idea as suggested above.
Of course, we use captcha.
With human assisted spambots, its no barrier, and most robots read it as well. Those who think captcha is fool proof are out of date, 10 years out. Captcha is like a screen on the front end, each step filters out a few potential spammers. We don't reject someone unless their user name is clearly out of line. Rules are not posted just to help spammers get around them.
We check new signups for duplicate ip's, internet providers, and a warning pops up if they have been banned before. Its far from fool proof, just another screen to filter out what we can.