[transphenomenal]

There was commerce between the Romans and ancient china that took around 10 years one way. I don't remember what was being traded, except for the silk from china, but it shows that distance and time are not absolute limiters for trading.

[MatthewPhillips]

Here's a good article about traveling to Alpha Centauri[1]. It posits that it would take 85 years best-case-scenario technology and 81k years using current technology.

Absent the discovery of new physics that allows us to travel through wormholes or something of that ilk, traveling to the other side of the galaxy for a vacation will, sadly, not be happening. Instead long-distance space travel will likely involve putting humans into cryosleep and then waking them up when they reach their destination; hundreds of thousands or millions of years in the future.

[1] http://www.universetoday.com/15403/how-long-would-it-take-to...

[redthrowaway]

Why send humans at all? By that time I'd assume we'd have reasonable AI; just send it along with a bunch of frozen embryos anywhere you please. The AI can incubate and raise the children. It could even terraform the planet until it was habitable. You wouldn't even need to explore; just send out probes willy-nilly. If they never reach a suitable location, then it's no big loss.

A fire-and-forget method of human space colonization is not only far more feasible, but also far more economical.