Real-life experiences and data are hard to find, which makes Andy Barbour's case study even more of a pleasure to read. You can find it at UK Solar PV Case Study. He profiles three installations including his own, all installed during Spring/Summer of 2010. Each has a peak rating of just under 4kW and uses a different panel manufacturer: Kioto, Sharp and Sanyo.
The three main charts in Andy's study show month-by-month comparisons of expected vs actual income, and shows that there can be quite a variance from expected income. The second page (see the 'systems in detail' link at the top) has considerable detail on each system, and examines energy output in kWh. The income charts show that it can be possible to outperform the estimate, but Andy's own installation has consistently underperformed. Is this because of his Kioto panels, his SMA inverter or his roof? The income is only slightly lower, however, so it shouldn't put anyone off installing their own.
This study goes to show that there is a real income to be made from a solar electric installation, but make sure that you get an estimate (of output and income) tailored to your house and proposed equipment.
Andy is keeping the charts updated on a monthly basis, so check back there often!