I love the Solitaire. Unusual for a Clan machine, it really works best as a team player, though. Unsupported, it's pretty easy to take down, but if you team it up with some big mechs then send it to flank it makes life really difficult for your opponent.
Like I said earlier, I think its one of the handful of specific mechs that are built to fight the IS rather than other Clans.
TRO3067 says the Diamond Sharks introduced it, and it was assigned to their Spina Clusters. I can't remember off the top of my head if Spina Clusters are the ones that guarded the supply lines to the Inner Sphere, but based on MoneyLovinOgre and Colt's comments, to me it would make sense if the Sharks assigned this to face Inner Sphere forces of some sort. Probably the
dezgra pirates that were trying to hit any Shark supply ships.