I had my 40D converted by LifePixel - they are great! One thing I ran up against pretty quickly, tho, is that a lot of lenses, in particular the 16-35 I was hoping to use for landscapes, have a nasty PITA "hot spot" of reduced exposure in the center of every shot [due to the way IR reflects inside the optics]. I'm currently looking at the Sigma 15mm to use on WA shots, since it is reportedly better. It would pay to research your current lenses before you commit to IR.
The 16-35mm is indeed not recommended for IR work. Here's a link on which lenses are suitable or not for IR photography: http://www.lensplay.com/lenses/lens_infra_red_IR.html
It seems to be a rather "old" list.
In the list the Canon 16-35mm is mentioned but not the MKII. Does it mean that the MKII does not have the hotspot problem?
I also do not see the Canon 24-105.
Are there any updated resources of what lens to use and what not?