The cap is..400% I think. 240 will be easily perma Hasten. I think my plant time troller is at..210 (with hasten) and thats enough for perma Chrono Shift as well.
As to how much is too much...once you have perma CS..any more, you wont notice. At all. Especially with Ageless being thrown about.
How much global recharge is too much..
Once you go near the cap it might be overboard. 
The development team and this community deserved better than this from NC Soft. Best wishes on your search.
Is the cap purely global recharge, or is it a mix of enhancement recharge and global recharge
ie.. I have a power that has 100% recharge after DR, and 245% global recharge through haste, CS and IO bonuses, and then I get another 45% from secondary mutation and a booster, then somebody on the team throws out an AM for another 30%.. so globally I have 320% and another 100% through enhancements.. is this putting me over the cap, or do I still have another 80% global recharge before I hit the cap?
Also, I am assuming that Alpha incarnate recharge bonuses are counted as enhancement bonuses and not global bonuses even though they effectively work globally, Is this correct?
The point at which it is "too much" is the point at which you've made unacceptably huge sacrifices elsewhere in the build, and/or the point at which having your powers recharge faster stops being beneficial. Both of these criteria are subjective to at least some degree, and also vary wildly depending on the build.
Edit: @Shadowhex, the cap includes enhancements, rather like the damage cap. The cap basically says you can never get a power to recharge in less than 1/5 of its base recharge time. Well, barring instant recharge effects like Enhanced Water Jet and etc, of course.
Thanks for the replies, things make a lot more sense now. Particularly the stacking of enhancement and global bonuses.. that is really good to know.
This relates to pretty much any AT that can really stack the global recharge.. in my case it is a sonic/time corrupter. When I-24 hits, and more specifically when the new ATIOs hit, I'm looking at a build that is pushing ~245% global recharge through powers and IO bonuses and I'm curious if it isn't going a little overboard. So the question stands, how much global recharge is too much? And to follow if someone could take on these questions I would much appreciate it: What is the global recharge cap? Does the recharge cap influence enhancement bonuses on individual powers after a certain point or does the global recharge just add on to whatever enhancement the power already has? For you theorycrafters, at what point does recharge start to loose out to other stats in a given build? Is it when you hit the point of the best possible attack chain?
Sorry for all the questions, I have played mostly melee types and generally my consideration runs something like: Is it enough for perma hasten? If no, then get more. If yes, that all I really need.