Linden Lab is tinkering with a set of Second Life graphical improvements for high-end graphics hardware. Dave Parks, software engineer at Linden Lab has been working on a set of features tailored to the Geforce 8 set of GPUs. Users without the required hardware would not suffer any performance reductions as a result of the new features.
The featureset (which is available as an experimental branch called shadow-draft in the viewer source repository, for the curious), includes hard Sun-shadows, per-pixel lighting, support for an uncapped number of point-lights, and lighting costs based on screen coverage.
The new branch has been minimally tested and found working on standard Windows, Vista, and some Linux systems, with decent frame-rates. MacOSX does not appear to contain the requisite level of shader support.
The code is largely unoptimized and experimental, and none of the new features can be enabled by those with older hardware. Firstly, older hardware just doesn't have the ability to handle the features, and if it did would likely be so slow that you'd be better off going and browsing the Second Life Flickr group instead.
At this stage, the feature is quite an early one, and Linden Lab has reaffirmed its commitment to supporting as broad a range of hardware as is possible, aiming for overall improvements that do not make performance worse on given hardware sets.
That said, degenerate conditions do exist for some hardware combinations (we've experienced them ourselves). If you've experienced reduced performance going from a non-windlight viewer to a windlight viewer (with Windlight features disabled), you should file your observations, settings and system specifications in Linden Lab's JIRA tracker, so that Qarl Linden and others can attempt to pin it down -- such cases may point to other correctable performance issues in the viewer code.
