One of the most limpid and luminous letters is `L.' -- Nabokov, Playboy interview (1964)

My first name, “Lillian”, has a double-“ell”in the middle, and thus, three “ell”s total in it. Count 'em: three. In fact, at one point, I was using the login “llllee” until people told me to cut it out.

Nevertheless, people seem to often omit one of the two middle “ell”s.

Well, not that I'm a fan of unigram statistics by any means, but the US Census Bureau has the following interesting data:

According to the 1990 Census, “Lillian” is the 98th most common female first name.
“Lilian” ranks 843rd.

Or, check out this data-visualization tool; typing in the prefix “LIL” (and judicious mouse placement) generates this:

The people have spoken!