Leaving aside the payback time (which is very long and usually longer than the lifecycle of many current panels), the life cycle assessment of PV is very complicated.
The technology is improving year on year, manufacturing processes are being developed, refined and simplified constantly and life cycles are extending.
You also have to look beyond the energy costs to the entire effect of PV development, manufacture, transportation and installation.
All PV technologies use non-renewable resources to varying degrees, with some resources in shorter supply than others. However, most of those resources are recoverable if a good end-of-life recycling programme is in place (which, by and large, it is not).
Also, many of the manufacturing process emit CO2 while some processes release other gases that either contribute to global warming or ozone depeletion.
In terms of
life cycle emissions analysis, PV does fairly well but is still nowhere near as good as hydroelectric or wind power. In fact, on balance, PV is about on a par with biomass. Obviously, there are differences in their outputs of specific gases - CO2, SO2, NOx - and particulates, but by and large they're about the same overall.
Of course, life cycle emissions analysis is only part of the equation. Nuclear does very well out of LCEA as various interested parties like to point out, but its outputs are nowhere near as manageable, despite the nuclear industry's claims. (And yes, that was a pro-nuclear site but the emissions figures match those elsewhere.)
If you don't mind waiting for a hefty download and can get through the science, then
Potential Health and Environmental Impacts Associated With the Manufacture and Use of Photovoltaic Cells is worth reading.
Personally, I think a lot of cowboys and "entrepreneurs" are jumping in to make a quick buck out of a fashionable and "eco-friendly" technology. You can be a good consumer and not feel guilty!
I still think the way forward is to use less energy in the first place, install the most efficient and eco-friendly solar hot water system you can afford (so no mains electric pump, no antifreeze etc) and only then consider what would give you - in your very specific circumstances - the most energy for the least impact and quickest payback.