I often push the boundaries of Inkscape and SVG, in order to hide Easter eggs in my comics, or when researching my Full Circle Magazine tutorials. But even I can't think of a time when I've ever intentionally *drawn* an invisible object.

There are plenty of times when I've drawn an object and then intentionally made it invisible (e.g. for text on a path or, most recently, when creating a SMIL animation path for my next tutorial), but I always draw them as visible objects first.

There are too many ways that an object could be "invisible" to catch all cases, but a simple rule of thumb might be that if both the fill and stroke are set to "none", have an alpha value of zero, or the object's opacity is zero, that the tool's default style is used. Combined with the earlier proposal about reverting to the tool's own style on start-up, this would lead to the following behaviour:

1) On starting Inkscape, creating a new image, or loading an existing one, all tools are set to "tool's own style".
2) While working on a document, "last used style" is used (unless the prefs are set to always use "tool's own style").
3) When a drawing tool is selected and the drawn object would be invisible (based on the heuristics above, and perhaps some others), the "last used style" is modified to match the "tool's own style".

It still wouldn't catch all cases - consider an alpha that's set close to, but not quite zero - but I think an approach like this would help new users whilst not particularly getting in the way of experienced users.