SolidComponents are a nice perk, aren't they!
I use them and have been happy. I've harassed Support several times to get more information and I don't think SolidStuff is something they have but don't spend much time thinking about. They recently renewed their contract for the service and I think the functions actually runs off of the Dreamhost Servers.
Good question about what constitutes a 'hit.'
In the three years I've been with Dreamhost, they've continually expanded what it offers to clients rather than taking away, so I'd be really surprised if this ever costs you anything extra out of your pocket. Recently they removed conuery limits for MySQL and are simply encouraging responsible use.
My biggest fear would be coming to rely on the SolidStuff and then Dreamhost deciding to discontinue the partnership. If you like and use the service, sent a positive comment to DH and let them know you value it as part of your service.
In fact, I would actually like to see the SolidGoodies we have expand. Check out the website and see the new things they've added.