If you haven't found The Photosynth Photography Guide (1Mbyte pdf), it's a nicely organized and useful overview of tips and tricks for shooting photos that make great synths as well as some tips for how to better navigate the synths on the Photosynth site. To make parts of this guide more accessible We'll be pulling out chunks to highlight here in the blog. This post will focus on:

Photosynth Viewer Keyboard Shortcuts
Try these keystrokes and mouse actions to get the most out of the Photosynth viewing experience.

Zooming and Neighbors
 
Scroll wheel Scrolling the mouse wheel zooms you in or out. The zooming is centered around your current mouse position.
+ or - Zoom in or out around the center of the window.
← or → Move left or right to a neighboring photo, when one is available.
↑ or ↓ Move inwards or outwards to a neighboring photo, when one is available.
u or j Move up or down to a neighboring photo, when one is available.
Tours and History
 
Spacebar Go to next photo in the spatial tour.
Shift-spacebar Go to next photo in alphabetical order by filename. (Depending on your camera, this is usually shooting order.)
. (period) Go to next photo in alphabetical order by filename. (Depending on your camera, this is usually shooting order.)
, (comma) Go to previous photo in alphabetical order by filename.
Z Go to the last image you were on. (Like Back in a Web browser.)
Z Undo z. (Like Forward in a Web browser.)
Fun with the Point Cloud
 
Ctrl Holding the control key down temporarily hides all photos allowing you to see the point cloud in all its glory. Dragging a halo with the control button down lets you spin around the entire point cloud. Try it!
P Switches among three modes: points, images, both.
Useful Shortcuts
 
Enter Center the current image
F Toggle full-screen
~ Toggle between 2D and 3D
M Go to the next 3D group in the synth
Y Toggles world-up verses image-up. This is useful when Photosynth has trouble working out which way is up.
Free Navigation (Only in 3D view)
 
A Strafe left
D Strafe right
W Move forward
S Move backward
E Move up
C Move down
L Rotate left
‘ Rotate right
[ Rotate up
; Rotate down