The rest of the forum will kill me on this, but no, I would strongly suggest you stay with iOS 4 for as long as possible. The second I installed iOS 5 my whole iPad 1 tanked. Apps crash constantly, and overall performance is worse. I also lost features with iOS 5, such as the ability to network print to non HP printers, or run banned apps, so you might want to consider those things too.
Will not "kill" the other poster on this, I am sure that his experience is true and that it was not good for his iPad. On mine it is great. Now what happened with mine and it may have made a difference is that I received mine as a gift and the other person erased all of his info and redid the iPad as a new machine and upgraded the OS. Since it was not an upgrade with all the programs and other stuff on it, that could have been why mine works great. I don't know, but it does work great.