Let's tackle the easiest question first. If you are looking to switch to Leopard on a minor maintenance release (1.0.x) that only contains a few bug fixes, I would recommend against it.
There will be a percentage of your customer base who will not switch to Leopard on day one. There will be a percentage of your existing customer base who will never switch. It would be a disservice to both of these classes of customers to force them to remain with existing issues because of Leopard rolling out.
In addition, Leopard has increased the minimum system requirements to run the operating system. This increase has removed a large number of older Macs from being able to upgrade.
As we all know, people hold onto their Macs for a very long time, and it is a fair bet that if you have an existing customer base, a surprising number of them are still using a Mac they bought several years ago (and potentially cannot upgrade to Leopard).
If the issue can be resolved in Tiger, by all means release the fix for Tiger. Forcing people to upgrade just to access these fixes will create nothing but ill will.