I've read through all the google documents on the subject, numerous times, and cannot see what I'm doing wrong. The keywords I'm testing are all 'active' (my billing has been set up and credit card accepted, as far as I can see).
I've been through the trouble-shooting page (https://adwords.google.com/support/bin/answer.py?answer=6105&topic=7055) and everything checks out fine.
Any suggestions as to what else I might be doing wrong?
Please.
use the ads diagnostic tool within your accout to see the reason why your ad isn't showing for a particular keyword. ("Campaign Management" tab, "Tools", "Ads Diagnostic Tool")
They show for a few hours before they stop and go in for manual review.
This is what happens normally. Sometimes they may escape a review for whatever reason but these days, that is not the norm.
Of course do use the 'tools' to check your ad status.