Quick Opinion: 1/week ain't bad... You've increased your risk, but it seems unlikely you've upped your risk percentage to a number that would bother you much. There is little to no data for people in your range of usage, so find a decent doctor and read up on the data yourself simultaneously.
Long-winded Opinion: Call me disrespectful to the medical community, but I have talked with almost no doctors (and I've looked - my family is rife with cancer...

) that are really educated in this field. Most are absolutists and just chant, "Don't smoke!" over and over... and refuse to discuss risks of occassional use.
If you want to educate yourself a bit, a good start is the NIH Web site and its tobacco/cancer related subsidiary - cancer.gov. There are some good links off of the CW homepage as well. However, if you want to actually read the real data yourself and get serious - then go to the National Library of Medicine's site (or drive your ass cross-country to their physical location near DC - and I'll buy you a beer and cigar before we browse the stacks), and start checking out journals - and getting on mailing lists with the doctors in the field.
If your research is like mine (which was extensive, but in no way complete), you will immediately notice one thing: As far as I know, there have been zero reputable or large-scale studies on occassional cigar smokers. There have, however, been lots that have users that smoke 1/day. According to most studies (information does vary) - smoking one cigar per day at least doubles the risk for oral cancers and esophageal cancer, and increases risk of cancer of the larnyx to about six times the level of a nonsmoker.
Going from 1/day to 3-4 a day is a massive jump. Whether the line where you are taking too much risk stops at 1/day or 1/week - is debatable and a matter of personal choice. After all my research, I scaled back from 1/day to a max of 2-3 a week on heavy weeks - and 1/week most of the time. Agree with the philosophical bent of Moki's post, but might disagree with the implication that 1/day does not substantially increase your health risks... but it depends on your definition of "substantial". (Do be careful with the data, almost every report you read is biased heavily one way or the other - and pay attention to the funder of the research as you read.)
What's your risk at 1/week or 2-3 a week? No idea. No one knows as far as I've researched (and I've looked - as I fall into the same category). The studies all tend to start at 1/day or higher - and most studies revolve around users that are 3-4 per day (people who smoke at this level have much much higher risk levels). Also, many studies fail to remove alcohol from the equation (yup - if you smoke and drink - you've found yourself a sort of "cancer synergy"!!) All we know is that a 1/week habit is less risky than one that is 1/day, but not by how much (remember, 6 times the risk of a nonsmoker isn't necessarily that high... still within "roll the dice" levels for many).
My advice: Find a doctor that knows what they're talking about more than me or any cigar group (I'd say we're a wee bit biased and perhaps lacking in credentials

). If you can't find a doctor that doesn't suck - then hit the books (preferably the source journals).
Last point: Talk to Moki's mom, she's got to be filled with patience for people trying to justify/rationalize doing things that are bad and/or crazy for themselves... and we should all email her and tell her how much Moki smokes so he gets grounded...
:sign:
Cheers,
- Oak