I should have bought this sooner -- this may be my favorite "toy" now! I had been researching and thinking about getting a Tandem Island for a while and finally pulled the trigger on a used one last year. I am an experienced kayaker, but have never sailed anything before -- and this is an ideal boat to start with. We figured it out pretty quickly after research and just getting it out on the water.
Here are some thoughts after having owned the TI for about 8 months -- I wish I would have known all of this when starting out:
-Learning this boat takes time -- read the forums, read the manual, test it on land. It's way more complicated than a kayak -- but you will be rewarded with a fun boat.
-It's big and heavy -- yes, you can car top it, but do yourself a favor and get a trailer and cradles for it if you can. We have launched it from the beach a few times, but usually just end up using a boat ramp for ease.
-It requires maintenance -- this will require more work than kayaks, of course, but it's not all that much, really.
-It is customizable and upgradeable -- Hobie does a great job with making parts available and you really do have the freedom to make some great upgrades to make the boat even better. You have so many options as there is no single way to make it work, rig the sails, etc. The forums will help you a lot.
-Buy spare parts -- make sure you have spare parts and tools for your kit. This is critical as there are a lot of things that can and will break (rudder lines, rudder pin, aka bolts, shock cord, etc). Again, look at the forums for this.
-Add some additional safety lines -- check the forums for idea on this, but there are some things that you need as backups (other than parts). This especially applies to the akas/amas as failure on these parts when you are sailing at speed or in heavy seas could be a BIG problem. Also think about a trailing line in case someone falls overboard.
-Know your limits -- yes, the same applies with any boat or kayak, but really watch the wind and sea conditions as you can get into a tough situation pretty quickly. I have taken this out in 15-18 mph winds and gotten up to 10 mph, but that felt like that's the outer edge of it's safe performance zone for me.
-It's great for overnights -- we use this for camping and can carry A LOT of cargo on the trampolines.
-Think about the setup -- this boat can be sailed by one person, but also think about how you want to have it set up for two people (who does what, etc). Mine is set up for me to sit in the back and I can do 90% of the work to sail it -- which is easier for me and better for my companions.
-Mount a GPS and watch your depth -- depth is a bigger concern vs kayaks -- especially with the dagger board, rudder and mirage drives. This can quickly ruin your day.
Bottom line: This really is a fun boat if you take the time to really learn it and make sure you are prepared. We have sailed this in a lot of different sea conditions and have even been far offshore with it. I am challenged by the boat and have been rewarded with a lot of fun, fast speeds and new discoveries. I can't recommend this boat enough.