A few things I've picked up on that might be of interest.
1) Roatan is definitely a place you can get Malaria. There have been recent reports (in the last few weeks) of several people picking it up.
2) Chloroquine is the CDC recomended prophylaxis.
3) Most places won't let you donate blood for a fair bit of time after you've been in Roatan.
4) Don't overdose on Chloroquine. Really. Seriously, be sure you remember when you took it earlier in the day. Accidentally taking it twice would be.... bad.
5) There appears to be some disagreement among reliable sources about whether it is of benefit to start the prophylaxis treatment 2 weeks ahead rather than 1. Given I wanted to know how I would react and have time to switch to something else if it was bad, I went ahead and asked my Dr. to give me enough to start 2 weeks ahead.
6) You will need to take chloroquine for 4 weeks after you are back home.
7) You really do not want Malaria. Read the recent Alert Diver article or talk to someone who has had a bad bout. It makes me really appreciate the philanthropists that are taking on this problem in the world.
8) While local meds may be good enough, and it may be protectionist fear mongering, there is reasonable cause to suspect the efficacy of anti-malarial medications you receive in less developped economies.
9) Chloroquine can cause some people side effects, but is generally well tolerated. I, and several others I've talked to have noticed odd dreams.
Obviously it is up to each person to make their own decision. However, I have a hard time imagining a situation where someone healthy enough to be diving would have enough risk associated with chloroquine to avoid taking it. I'm not saying it can't happen, I'm saying I can't readily imagine it.
Also, if you haven't had a tetanus shot in the last decade, it probably is a good idea. Thinking about it afterwards, I'm annoyed at myself that I didn't already have an updated one, especially considering that I've seen people scratch themselves on wrecks and such.
Your doc may not reccomend all of the CDC proscriptions, but most people seem to think a Hep-A shot is also worthwhile.
Just what I've learned researching over the last few months.