We have used solar panels on several boats over the years and found they work well for our needs.  You will find there are as many opinions on how much wattage you need, panel placement and panel types as there are sailors.   

We currently have one 30 watt hard panel mounted on the stern pulpit of our W28.  It handles all of our electrical needs for cruising in the Puget Sound area.  Our boat has a Seafrost 12V coldplate refrigeration system, we have switched all of our lighting to LED's and use a 12V Raymarine Grand Prix tiller style autopilot.  We have the basic 12V instruments; DS, KM and a VHF radio.  Our biggest electrical draw is the Refrigeration at about 15 amps per day, our 12V fans draw 1 amp per hour.  The LED lights draw only about .10 of an amp per hour per light !!!

In the late 80's we cruised to Mexico and the South Pacific on a different boat that was equipped with two 55 watt solar panels also mounted on each side of the stern pulpit.  That boat had an Adler Barbour 12V refer system, incandescent lighting, a SATNAV , Autohelm 2000 tiller style autopilot, also several 12V fans, basic instruments; DS, KM, WS and VHF.  On that boat we found the panels would keep up with the electrical needs (refrigeration and fans) during the day, but we had to charge the batteries with the alternator/engine every other day if we ran the Refer over night.  The masthead anchor light and tricolor lights ate up 1 amp per hour and were easy to forget to turn off in the morning!

We have found that mounting solar panels off of the stern pulpit gets them out of the way on deck and keeps them out of shadows from the mast, boom and rigging.  There are a couple of photos of our W28's current installation in our photo album.

Kevin 

Sundowner came with about 200w of solar.  Two panels mounted over the main hatch but forward of the dodger and two panels mounted on the side rails which were then "raised" and "lowered" with a length of cord attached to the boom gallows.  We've ditched these solar panels as they were very old and inefficient in terms of size/watt.

I've invested in a MPPT controller for our panels.  These increase the efficiency of solar panels but they are expensive.  For a boat with limited space to mount panels, I think this trade off is worth it.  We went with a 30amp bluesky controller.  The controller is attached to the house bank and regulates the charge current.

We have 5 x 100w flexible renogy panels.  I'll be mounting them soon.  We got the stern tower from Bud and I'll mount two ontop of it and I'll put two more on the rails where the previous panels had been, giving us about 400w of solar.  The fifth panel will be "in case" we need it or if another panel dies or is damaged.  Haven't really decided yet.  At first I thought about mounting it ontop of the dodger or something. 

Try to keep the panels away from the sails and rigging or the boom.  Any shade severely cuts power production. 

We also installed a battery monitor for watching what is going on power wise.  It has been a neat gadget to understand the power draw and needs of the boat. 

Caution:

How much solar wattage and what type of controllers you use on your boat should largely be determined by "other" factors and not just what others are doing.  A 400w solar bank is inappropriate for a boat with 50a/h worth of battery power.  Like wise it is silly to assume you can run a fridge in the tropics off of a single 30w panel.  What type of lights, electronics, and what type of power consumer you are will determine these things for you.

I have two 125w Kyocera solar panels. After about 8 years I noticed one was putting out the correct voltage, just no amperage.  I think the problem stemmed from it getting broadsided face on by a big ol green water breaker. When the wave hit it sounded like someone smacked the panel with a baseball bat.

The panels supposedly had a 20 year warranty. I contacted Kyocera expecting to get some sort of excuse.

Surprisingly, Kyocera shipped two new panels to me via FedEx, paid the customs duty and included a preprinted, prepaid shipping label to return the old panels in the box the new panels came in.  Hardly any questions asked. All I needed to do is fill out an RMA form with the serial numbers to establish date of manufacture and voila!  I had replacement panels in hand within about a month. I would have had them sooner had not Guatemalan customs held them up demanding more duty than Kyocera was used to paying.

I'll never buy anything solar other than Kyocera.