So I'm writing a small Windows application, and I'm seeing many places where I could make life easier for touchscreen users (through things like swipes and multi-touch in Windows 7). However, is it worth it? Are touchscreen computers widespread enough for me to care? Or should I wait a year or two?
I can't actually disclose what I'm writing, but let's just say it's an interface enhancement for power users. :)
In my opinion they will certainly be widespread. If not on desktop computers, then think about netbooks and tablet PCs - they can all benefit hugely from such functionality.
It depends on your software though. For example, if it deals with some kind of documents, then it is probably worth it.
Touchscreen PCs are still rare, this article for example estimates their market share at less than 0.1% in India (haven't found any recent estimates of worldwide numbers, but I have no reason to think they'd be enormously different). However, the effort to support them well may be low enough, with possible upsides of gaining niche appeal among users of such computers and of being well-poised if and when they suddenly take off in the near future (and your competitors are scrambling to retrofit good support while you already have it).
This is a personal opinion, not a definite answer.
I think that if you have a situation where the added ease-of use is justified, I would start right away. You get the double bonus of working on cool interfaces, and also being ahead of the curve with something that's very likely to be used more in the future.
But you'll have to weigh in your other concerns, such as do you have the ime to learn this and can you afford the learning/training time in your budget.