In the track view window, the Move Keys Horizontal and Vertical Buttons should restrict the movement of keyframes on the horizontal (time) or vertical (value) axis, but do not in my version of 3ds Max 2012 SP1. Work around include using the dope sheet or using the Keys > Slide or Keys > Scale Value menu items.

Can anyone else confirm this?

Known issue - discussed here a number of times, most recently here.

2 quick points. This is more a version-specific issue than an Animation one (although related to animation). The Max2012 forum would have been a better place to ask about it.

Always search first - often much quicker than waiting for someone to reply as most questions have been asked a number of times before.

Max 4.2 through 2013.
XP-64 (SP2)
NVidia 9800GTX-512 (Driver 266.58).
Core 2 Quad Q6600 2.4GHz, 8Gb Ram, DX9.0c.

I must not have been using the correct keywords. Thanks for the links!