Performance of IN (...) vs. = ANY array[...]

Greetings:

I'm running 8.1.4, and have noticed major differences in execution time
for plpgsql functions running queries that differ only in use of an
array such as:

slower_function( vals integer[] )
[query] WHERE id = ANY vals;

faster_function( vals integer[] )
vals_text := array_to_string( vals, ',' )
EXECUTE '[query] WHERE id IN (' || vals_text || ')';

In general, there are about 10 integers in the lookup set on average and
50 max.

What are the advantages or disadvantages of using arrays in this
situation? The = ANY array method makes plpgsql development cleaner,
but seems to really lack performance in certain cases. What do you
recommend as the preferred method?

Thanks for your comments.

--
Benjamin Minshall <minshall(at)intellicon(dot)biz>
Senior Developer -- Intellicon, Inc.
http://www.intellicon.biz