We started DS on SWMNBN's routines at about 3 weeks old, but stopped reading the book when we got to know him better and could work stuff out for ourselves.
DS is now nearly 18m, and still having a morning nap and a lunchtime nap - total of about 2h45 minutes during the day. He sleeps for 11-12 hours at night - bedtime is between 7 and 8, depending on how slack I am. I work full-time, so often elongate bathtime etc because I like the time with him.
DS rarely seems sleepy at nap time. He sometimes chats or sings for a bit when put down for a nap. If his morning nap is pushed back an hour or two (rare) this doesn't seem to be a problem. He also seems fine with later bedtimes when they happen. These things lead me to think he may be ready for less daytime sleep.
However, some days he goes down for his nap at 9, goes straight to sleep and sleeps for two hours. Which makes me think he still needs all his daytime sleep.
Anyone have similar experience? It's not like it's a problem, but it does limit morning activities somewhat - and I just expected that he would have dropped it by now. Everything was so much clearer when he dropped his afternoon nap!