I wouldn't bother with this kind of service and definately wouldn't pay.
I've read somewhere that most of the major search engines won't even accept your site unless it has a link from another site. If you have some good links then you'll get spidered through them.
The amount of links to your site from other similar popular websites determines your popularity. If you get a link from a popular website, you'll pretty much get indexed without having to submit your site.
So if you want to get indexed, I would just start getting some site links.
I usually get indexed from forum posts like this one.
Also, some site will give you a boost if you get spidered from a link from another site.
Most of the submission sites submit you to FFA which do little good.
I think these submission sites make a nice looking "bonus." That is probably why yahoo (I think you said) uses them.
Just my two cents.
John Karnish
Tripple Your Resell Right PRofits