Is ProQuest a reputable company? What are the possible benefits or consequences of submitting my dissertation to ProQuest?

My university recommends submitting dissertations to ProQuest. I am wondering about the practices and academic reputation of this company, and whether or not it is in my best interests to follow the recommendation of my institution.

Does ProQuest support academic work? Do they charge exorbitant fees to access their content?
I don't think Proquest is really a publisher so much as just a repository.  They don't make any editorial choices about the material they host. 

I don't have any information about their financials, but accessing dissertations through them is moderately difficult and expensive.  (I think getting a copy of a thesis from them is on the order of US$50.)  I think of them as the dissertation archive of last resort - I would only order from them after exhausting all other options (author's website, university's library, etc).

My feeling is that you might as well submit your thesis to them, since it is good to know that future researchers looking for your thesis would always have Proquest as a fallback option.    However, you should make an effort to make your thesis available through more convenient (and free) means as well.  Post it on your professional web page.  If your field uses arXiv or a similar open access repository, upload it there as well.  (Since you will presumably be publishing papers and/or books based on your thesis, check first that the relevant publishers are okay with having your thesis available for free online.  Probably the major journals/publishers in your field will have similar policies.)