I don't raid at all and most of my groups are either Pick ups or 3 or 4 man based on who from my small family style guild is online. As for how Necro's stack up to other classes? I am lvl 90 with 202 AA's. 113% Crit, around 30% crit bonus, 35.5% potency and 1088 ability mod, three master pets and a mix of adept expert and master spells. I average about 7500dps zonewide and have spiked upwards of 13-15kdps on single fights without using Lifeburn.
My typical guild group is myself, a Templar, Ranger and a Shadownight, all lvl 90. With this 4 man set up I usually trade off the number 1 dps spot with the Ranger who is fully mastered and has about even gear with me. once I get all my spells upgraded to at least expert I should have no trouble holding the top spot in that group.
I got lucky while I was leveling up and got into a pick-up group with a bunch of hard core raiders who just needed a 6th to fill the last spot in thier group and didn't really care who it was. I did ok in that group and since then I've had some really good luck getting picked up for groups by some of the best geared charactors on the server. While grouped with them I've hit 13-14k parses on single fights and ended up 5th on the parse right above the healer... lol For the average pick up group with average players though, I never have trouble holding the number 1 or 2 spot on the parse.
In all honesty, it really depends who you're grouped with. The average player really isn't very good so if you pay attention and do your best on every encounter you'll shine more then a charactor with insanely great gear that just coasts through. It's the little things like quickly rezing someone who dies during an encounter or throwing a vampiric orb on a tank when he pulls a room full of mobs to help out with an extra tick or two of healing that will get you noticed and make sure you are remembered. I did find it kind of satifying though, when i got into a pick up group last night with 5 guys from my servers two top raid guilds and my little noob guild Necro took 2nd on the zonewide parse. Thats not bad for a caster thats still wearing a lvl 79 robe.