Im not the General Consensus (they are all fixated on Optimization)
The Soul Knife is a ok class, on roughly the same level as any of the other 2nd Line types (Monk, Rogue, Ranger, Duskblade etc)
If the rest of the group are normal players then be a normal player
(While Not currently as its on Hold) I play in a Group that has a Soul Knife in it and he does fine, Other members being a Druid, Cleric, Wilder, Psion and Ranger
(of Course we're all normal players and not worried about tweaking a PC to the max or is its performing the most DPS, the Psion has a +2 LA for instance)