dnscache performance still applicable today?

Why I asked: dnscache's log file has stats lines like:
2009-05-24 18:42:48.254665500 stats 2098047 158736598 190 0

According to dnscache log file description at 
http://www.dqd.com/~mayoff/notes/djbdns/dnscache-log.html#stats
the third number after stats (190) means:

udp-active  	The number of queries that dnscache has received via UDP 
but not yet responded to or dropped.

Am I right in assuming that dnscache's single thread of execution 
becomes its main bottleneck, so it has to delay query execution while 
processing current requests?

Probably when dnscache was written the load on the Internet was lighter, 
and SMP computers were rare, unlike today. Any advancements in this area?