Personally, I never saw exactly what was better about Leopard over Tiger - save for this "eye candy" that everyone recommends turning off. I mean, I'll give Leopard some points for having better software support; but that just comes due to the fact that it's the more recent of the two, and at least for me, Handbrake is the only application I can think of at the moment of which the Leopard version has features that are of benefit.
On Tiger, I have TenFourFox for browsing, TenFourBird for email, iTunes for music and VLC for media, Audacity for editing, Office 2004 for documents; I rarely touch other applications, and these all do the job I need them to. I recognize that not everyone is as simple as I am in computing needs, but I see no need for cover flow in Finder, Stacks or Spaces, or any of the other features Leopard touts over its predecessor.
I guess it's all a matter of perspective. I use the finder features of Leopard pretty heavily, and find myself somewhat cramped when I use Tiger seriously.
Office 2008(or newer) is an absolute necessity for my work as I need to both read and edit XML documents. Of course, the requirements for O2008 are massively overstated, and it will actually run fine(albeit slowly) on a G3 under Tiger.