We have had two SunMate Solar Heating Panels installed on our home addition, November 2008. One is installed on our new master bedroom and the other on a family room. Together they are heating an area of over 900 square feet. To add perspective the rooms are well insulated with R26 or so in the walls and R50 in the ceiling. The panels are facing approximately 15 degrees east of south in St. Louis, MO.
On a day with full sun and the outside temperature in the low to mid 20s the two panels will bring the room temperature in the morning from about 60 degrees to 68 degrees. On those days, the furnace will not come on until late in the afternoon. On warmer days the units will provide heat even when there isn't full sun.
As long as your expectations are not too high, these units perform well. At the current cost of gas in the St. Louis area, these units will probably only give us a 5% to 8% return on our investment due to the fact that we have sunny days less than half the time. But this is one way you can do your part to reduce carbon emissions.
Note that there are a few errors in the installation manual, but Paul at Environmental Solar Systems has been very helpful in resolving any issues.