Likewise here after 18 months of the Desire and many cases tried!!
I just bought some aluminium cases from PDair and cable tied them to the stem. Easy access to the Defy and no need to worry when it gets a bit wet. Not much bigger than a Garmin 800 too.
Battery life seems a lot better than the Desire too and works well the Polar Bluetooth HRM (Xmas present after my Zephr died).
Motorola Defy Plus (Motorola Defy+) with Android 2.3.4.
Waterproof, shock proof and dust proof; a natural partner for Run.GPS :) No need to worry about cumbersome cases.
So far, so good... everything seems to work fine, i.e. quick and accurate GPS signal.