I heard a longstanding web dating owner / operator of an Irish site on the radio discussing online dating about a year ago and they said the biggest impediment to meeting someone is the unrealistic parameters which the prospective daters set. In mens' case it was always about seeking a MUCH younger partner ( 40 / 45 year old men wanting to meet 25 - 30 year old women and 55 - 70 year old men wanting to meet women in their 30's and early 40's. Thus ruling out women their own age who might be perfectly lovely and with whom, presumably they would have much more in common.
For women their pre-requisites were an equal or superior educational standard. As women are much more likely to have higher education then this creates a very limited pool and of course rules out large numbers of great potential partners who might be tradesmen or workmen etc who might not have graduate or post grad status.
The other impediment was a reluctance to travel outside of their area / county.
Apparently a lot of time was spent administering a reality check to many people when deciding their 'Would Like To Meet' descriptions.