My two year old home-built PC is struggling to run Lotro as smoothly as I would like. I experience a lot of stuttering in crowded areas such as Bree and Archet. Lowering the graphics resolution helps a lot at the expense of prettiness so it is almost certainly a graphics card defficiency. I have noticed that playing on the Laurelin (Role Play) Server is less jerky than playing on Evernight (non Role Play). I guess there are fewer players on the role play server. Fewer players means less crowds and less effort at rendering for my poor graphics card.
I use the excellent utility FRAPS to measure frame per second (fps) rates - it can even do screenshots for games that don't have this facility. Graphics card reviews give much space to comparing average fps between cards but from a players point of view it is not average frame rate but minimum frame rate that affects game experience. I would love to have frame rates consistently above the 60 frames per second refresh rate of my LCD monitor but I have noticed that as long as a game stays consistently above 30 frames per second it is very playable. My 7300GT DDR3 ( a sort of turbo charged 7300GT) is not a bad mid range card. It gives frame rates of above 40fps in high quality mode in many areas of Lotro but it has an Achille's heel which causes the frame rate to drop to zero whenever I enter and move around a crowded area.
The problem I think is that my card has only 128MB of graphics memory and this is not enough space to store all of the graphics textures in high detail mode. Once graphics memory fills up there is a long delay while textures are read to and from main system memory giving rise to a stutter.
I have settled on a compromise which is effectively high quality graphics mode but with texture quality set back to medium. This gives excellent playability outside of towns and OK playability in towns.
I would love to be able to play smoothly and fluidly at higher quality graphics but I think a new graphics card with more memory would be required for this. I am not due to replace my homw built PC (Athlon XP3500+ 2Gb RAM) for another year but I am tempted by the €120 Geforce 8600GT / 256Mb.