Maybe it's just me but in between concentrating on ukemi, concentrating on the technique/principle that we're working on, concentrating on what the Sensei is trying to show you, flying across the mat at a fair old rate, sending someone else flying at a decent rate, getting the hell out of the way so that you don't get clobbered by an incoming strike, getting the hell out of the way when you inadvertantly step into the path of someone who's flying your way, etc. etc.
Where is the time to get bored?
Let's face it. Aikido is non-stop fun.