If I upload a draft of my paper to arXiv, will I still be able to publish in an IEEE or ACM publication? Since IEEE/ACM will eventually own the copyright of the papers they publish, and since they charge for access to papers, if I have a paper on arXiv is that a problem for them?
As @Jukka Suomela has indicated in the comments, yes, you will.

The relevant policy for IEEE (from http://www.ieee.org/documents/ieeecopyrightform.pdf) is:


  8 . Electronic Preprints. Before submitting an article to an IEEE publication, authors frequently post their manuscripts to their own web site, their 
  employer’s site, or to another server that invites constructive comment from colleagues. Upon submission of an article to IEEE, an author is required to 
  transfer copyright in the article to IEEE, and the author must update any previously posted version of the article with a prominently displayed IEEE 
  copyright notice. Upon publication of an article by the IEEE, the author must replace any previously posted electronic versions of the article with either 
  (1) the full citation to the IEEE work with a Digital Object Identifier (DOI) or link to the article abstract in IEEE Xplore, or (2) the accepted version 
  only (not the IEEE-published version), including the IEEE copyright notice and full citation, with a link to the final, published article in IEEE Xplore. 


For ACM, from http://www.acm.org/publications/ACM-PubLicenseAgreement.pdf:


  (b) Furthermore, notwithstanding the exclusive 
  rights the Owner has granted to ACM pursuant to Paragraph 2 (a), 
  Owner shall have the right to do the following: [...] (v) Prior to commencement of the ACM 
  peer review process, post the version of the Work as submitted to 
  ACM (“Submitted Version”) to non-peer reviewed servers...


This answer is current as of August, 2014.