Dunno - it seems that if the service is enabled it shows up in all my browsers. I tried it in Camino, Opera, Safari, Chrome, and Firefox and the service is there when text is selected. What makes you say it is flaky? It seems that services has been pretty consistent for me throughout many applications.
When I use it from Firefox in Snow Leopard, I get a message (from TextEdit) that says,
There might be an internal error or a performance problem, or the source application may be providing text of invalid type in the service request. Please try the operation a second time. If that doesn’t work, copy/paste the selection into TextEdit.
Oddly, it works fairly well on my Leopard machine.
From Chrome, the service does not appear. [EDIT: This fixed itself when I updated to Chrome 7. Now I get unstyled text, like Opera, which is fine.]
From Opera, I get plain, unstyled text with no links or images.
In Safari, it works fine (Styled text, links, and graphics.)
Like I said, your mileage may vary. Services support is usually good for OS X applications. Ports of Windows apps usually have lousy Services support.