Ben, If a DSLR is what you want, then go for it, but I doubt you will outgrow an e-pm1 (or any Micro 4/3 camera) any time soon especially if you are a fairly new diver/photographer. And from what I've seen it's not "a little bit more money" for a DSLR, even the lowest cost housing for a DSLR will cost you over double that of a housing for e-pm1, and that doesn't include a port, by the time you add that in your are probably triple the cost. Even with a Zen or Precision dome and the PT-EP06 housing you are still right at around $1100 total. You won't find a DSLR housing with a dome and flat port anywhere near that. Right now you can do quite well with a e-pm1 kit that will start around $2000 that can include camera, housing, and single strobe setup. Add a wet macro lens and adapter and you can do some awesome macro for around $250 more. Add a dome and wide angle for around $1200 more and you have great wide angle. Either way you will come in way below a DSLR with the same capabilities, I'd estimate at least half, maybe more depending on exactly what you choose to buy. And the D7000 body is over twice the e-pm1, and the 7D is triple, so again, not a little more, unless double or triple the cost is "a little more" in your view. So take a D7000 body ($1100), add any $700 lens you want (say Tokina 11-16mm), and the lowest possible cost housing which is probably an Ikelite housing and port ($1800 or more if you get the correct dome port for the wide angle lens), and you are already at $3600, which is enough to get an e-pm1, PT-EP06 housing, both the Precision and Zen domes, and the 8mm and 9-18 zoom (camera $399, domes $499 each, Pany 8mm $639, and Oly 9-18 $699 which totals out to around $2735 (all prices were quick Amazon and or BlueWaterPhoto lookups, not necessarily list prices in some cases).
I was on a week long trip last week with a mixture of compact and DSLR users though I was the only Micro 4/3 user with my new e-pm1. And while the housing for the e-pm1 isn't as small and light as some of the compact camera housings, you will still at least double your packing size/weight if you go with an DSLR. This may not matter to you, but when travelling, weight and bulk makes a big difference. I was able to bring all my photo gear including camera/housing/strobe/tray-arm/focus light and other misc parts in a single carry on bag that also included some clothes, my regulator, and a few other misc items. This would be very difficult to do with a DSLR setup, and I doubt you'd get much room for anything else if you were able to pull it off. And so far while I haven't reviewed all the photos from the DSLR users, from the ones I've seen so far I can say that some of my photos are easily as high of quality and I doubt that if someone didn't tell you that you could tell the difference between my shots and those made by the DSLR users (and they weren't using entry level equipment, they were using much higher end DSLR equipment and top end lenses).
...i live in okinawa.
