20mm on the GH1 is roughly equivalent to 40mm on a 135 film stills camera (e.g. traditional 35mm SLR), or on a full-frame digicam. The 4/3rds sensor is approx half the area of full-frame (or 135 film), so simply double the focal length when thinking of the equivalent lens for the same field of view on full-frame.
The Panasonic 20mm f/1.7 is a very good all round prime lens in terms of focal length and light gathering; it's a fast, wide-standard. The GH1 is software matched with it to correct for some distortion and false colour (including in video mode) so images will be sharp. It is very small and light, and so is ideal for travel. It's an electronic lens, so manual focus and manual aperture control inputs are indirect (the latter via the camera). The focus motor is not silent and may be picked up by the onboard microphone in quiet environments; it's also not the quickest AF.
If you can have only one lens to start with you might want to think about picking up the GH1 with the 14-140mm "kit" lens first. Its only real downside is that it's slow (f/4 - 5.8) so you'll struggle for light indoors and at night (more ISO so more noise), plus not so good for "bokeh". For outdoor work, though, it's brilliant. Focussing is fast and silent.
Lots to think about, so don't rush unless you have to.
Hopefully someone can show a video capture of scenery using GH1 + 50mm. I wanted to see how it looks like since it's focal length will be 100mm based on a 2 crop ratio.