As the newbie, I thought I throw in my 10 penneth!
Just spent three weeks in Scillies using the 188c I bought a month ago. I also went for the Blue chart CD for the south coast and a PC/GPS power/data adapter. This setup allowed all waypoint creation with the click of a mouse on the PC. Then with route planning from Penzance across and some inter island routes also completed on the PC, another click of the mouse transferred the whole lot straight into the GPS, which was also on the desk and powered up. This allowed me to get to know the GPS and how to use it whilst 'sipping my Horlicks!', before needing it in anger on the RIB
As others have said, to get the tidal data working and some other nice software changes, you either need a chip upgrade, or in my case you just download the changes direct from the garmin web site, run the file and the GPS auto updates. The update took less than 2 minutes.
In use, the 188c is the dogs b**s. Its easy, reliable and the colour display is good. And now that the price is down to less than £900 and falling, its just getting better.
Cons?...the depth/fish finder works well enough, BUT, the transducer is transom mounted on an adjustable plastic bracket that clicks it into place and is designed to give way under load and flick up. However I have found that on high speed runs or lumpy seas, the bracket allows the transducer to flick up just a little too easily, requiring a push back down before shallow waters are reached! However, still v. happy with it and would recommend it.