Tmux configuration to enable mouse scroll and mouse panel select, taken from: http://brainscraps.wikia.com/wiki/Extreme_Multitasking_with_tmux_and_PuTTY

.tmux.conf

# Make mouse useful in copy mode
setw -g mode-mouse on

# Allow mouse to select which pane to use
set -g mouse-select-pane on

# Allow mouse dragging to resize panes
set -g mouse-resize-pane on

# Allow mouse to select windows
set -g mouse-select-window on

# Allow xterm titles in terminal window, terminal scrolling with scrollbar, and setting overrides of C-Up, C-Down, C-Left, C-Right
# (commented out because it disables cursor navigation in vim)
#set -g terminal-overrides "xterm*:XT:smcup@:rmcup@:kUP5=\eOA:kDN5=\eOB:kLFT5=\eOD:kRIT5=\eOC"

# Scroll History
set -g history-limit 30000

# Set ability to capture on start and restore on exit window data when running an application
setw -g alternate-screen on

# Lower escape timing from 500ms to 50ms for quicker response to scroll-buffer access.
set -s escape-time 50

putty-config.txt

Terminal -> Bell -> Action to happen when a bell occurs = None (bell disabled)
Window -> Lines of Scrollback = 1000 (For the quick "Oops, what did I do" moment)
Window -> Reset scrollback on keypress = check
Window -> Reset scrollback on display activity = uncheck
SSH -> Remote command = tmux a -t base || tmux new -s base (if you're going to use this connection for tmux)
SSH -> Protocol = 2 only
SSH -> Auth -> Attempt authentication using Pageant = check (Most Important One)
SSH -> Auth -> Private key file for authentication = c:\full\path\to\rsa.ppk
SSH -> X11 -> Enable X11 forwarding = check (Important if you use X11 applications that need to display to your laptop.)

(copy/paste with mouse in putty should be done holding shift key)

When I select text inside tmux it highlights it until I stop dragging then immediately deselects it.
So I can see no way to mouse select text and copy it.

Note: Shift-Drag is not really an option as it doesn't respect tmux panes.