Dr. Hilary Clayton has mentioned stuff about heat getting trapped in boots and recommending cold hosing after riding, especially when using SMBs.
Here's an article on some guy doing some stuff, it's all unpublished though..
I don't want to post weblinks to the articles I have though because they are all accessed through a proxy server... but I will post some cool articles I have found...
Equine Veterinary Journal
Volume 36, Issue 8, pages 769–771, December 2004
Influence of support boots on fetlock joint angle of the forelimb of the horse at walk and trot, Kicker CJ et. Al.
This one basically says that support boots DO reduce the extension of the forelimb, but concludes to say who knows what the long term consequences of this are and that it may impede healing and actually do more harm than good.
Volume 20, Issue 8, August 2000, Pages 503–510
Evaluation of shock attenuation in the forelimb of horses wearing boots and wraps Luhmann, MA et. Al.
The abstract to this one:
High frequency, high amplitude shock waves, believed to contribute to detrimental joint and bone changes, are generated each time the hoof strikes the ground. The purpose of the present study was to compare the shock attenuating capability of athletic support boots and traditional cotton wraps (polo wraps). Accelerometers were attached to the hoof and third metacarpus of five horses. Peak deceleration and asymptotic frequencies were measured at two speeds (3.5 mls, trot, and 6. 0 mls, gallop) under the following conditions: control (no boots or wraps), cotton wraps, and two athletic support boots. Leg supports did not reduce shock in the third metacarpus. In fact, support boots increased the asymptotic frequency measured in the third metacarpus. This result could be explained if the leg supports were acting to stiffen the limb, thereby increasing the spring constant of the leg support-limb system.
And I still can't find the darn presentation!... *angryface*