Any issues with fuel injected motors, specifically tbi?
I run it in my crankcase, fuel, and straight into the topend. I usually run a can through the fuel every few tanks on my DD (vortech 350), and a can in the vac line every couple years. I run fuel treatment pretty liberally, but I'm used to killing the engine by sucking ice crystals through the filter due to condensation freezing at about -25*. If you see any Iditarod or Iron Dog coverage, you'll see Heet getting shipped in by the pallet load (cold climates use a ton of drying treatments to battle condensation).
You really can't use it too often, it's more of how often you want to buy it. I wouldn't recommend going much over the manufacturer's recommended concentration though, at least not in the oil for any prolonged time(you might break it down). I have used a ~25/75 mixture of Seafoam to 5-30 to wash out my ATV engine after rolling it repeatedly down a river. (pictures cuz they're cool

, you can see my passenger tires behind the Honda in the second picture)
I used my can of Heet in the gas tank (after dumping the contents), so I used the Seafoam to absorb as much water as possible from the crankcase while I ran just above idle for about a minute. I dumped it out and put 15-40 with about 8oz of Seafoam to drive it back home. Changed the oil at home and hardly saw any signs of moisture contamination.
We run it every tank in our two Honda snowblowers we use for commercial roof snow removal. We bought them both used at a garage sale in the early 90s and have been used about 7-8 months out of the year since then. They still fire right up like they're brand new (part of that is that they're Hondas), rarely any condensation issues or fouled plugs. To emphasize the abuse those motors go through: On a few occasions, employee's have brought their own blowers onto the job (like when we're removing 100,000 sq. ft. of 3' deep snow). I've never seen another snowblower last through an entire day (even seen cracked blocks before).
That became more of a Honda sales-pitch

. They're just really awesome small motors. Anyway, we run Seafoam religiously in all of our equipment and it's always treated us very well. Never had any issues or poor results.