OmniWeb 4.5 - which will have the functionality previously referred to as being in 5.0 - will be available later this quarter and will be a free upgrade for OmniWeb 4.x license holders. The Omni Group is making early versions of OmniWeb 4.5 available through the Sneaky Peek preview program.
OmniWeb 4.5sp2 is available to download now. Check out the release notes for known issues and changes applied to each sneaky peek. OS X 10.2 or higher is required, as is a license for a previous version of OmniWeb 4.x.