Yeah, just a little bit of experience :P
I get best results using horizontal, most of my installations have either a PacWireless 4 (10dBi) or 12slot (15dBi) waveguide. Some omni-directional (double sided) for repeaters.
They seem to perform a lot better than verticals over water. Plus they have a bit more horizontal coverage which is useful for places with a large tide difference (not that you'll have this issue on a lake).
Many people suggest diversity when running links over water - I agree if you're running greater distances. Otherwise no need if users are just using standard client adapters within 500m or so.
On another note I've further developed my little hotspot user interface. http://picasaweb.google.co.uk/ben.johns ... evelopment
. Some day I'll make a public test available - currently the test server runs transactions against the actual bank and influences other external entities.
I'm thinking about integrating PayPal - is their premium 'gateway' product worth the money? It's a fair whack more than what I'm paying a local bank for the CC only stuff. Really I just want access to Direct Debit/BPay/PayPal credit facilities - don't need CC since I'm already paying <2% per transaction.