If you're looking at things pragmatically (and not, say, dogmatically) then you can rely on JavaScript running on a client machine.

Does it run on every machine? No. Can you ignore the part of the market that doesn't have working JavaScript in the browser? Sure you can.

If someone doesn't have JavaScript, he's either extremely paranoid (and belongs to a really minor minority) or using hopelessly outdated browser (a minority that most likely wouldn't be a good customer anyway).

I don't think any of the major websites (like gmail, google maps, facebook, hotmail, twitter) would work if JavaScript didn't run on the client. If Google Maps can afford to not care about such clients, so can you.