The only vinyl I try to put on CD are the ones that have not (and ARE not) likely to be rereleased on CD in the first place. It is worth the $15 or so to get the clean, original sound from the source recordings.
It also depends on the ultimate quality you want to get. I use a Bang & Olofson turntable and cartridge to get the absolutely best source sound to start with. As mentioned you need to have the turntable plugged into the phono sockets of a good quality amplifier (this converts the magnetic cartridge input to a correct EQ.)
Unless you want the rumble and scratches and "pops", you will need a sound editor. There are several automated ones but I use the sound editor that comes with "NERO Burning ROM". It allows you to take out a click or a "pop" with the smallest amount of loss of music. A scratch on an LP may make a noise that lasts a few milliseconds but if you don't remove it, it will piss you off forever.
As I say, it depends on how much quality you need and the time you want to spend doing it.