In response to Pekka's answer:
- A large number of users can gain reputation much faster than an individual SO user. Some of us have to sleep, and do things other than Stack Overflow.
In theory, yes. In practice, there is a rep cap. And also the truism that two average programmers don't equal one exceptional programmer. If the strategy is to throw enough lousy answers onto the site that the account hits the cap via sympathy votes, it's abuse - regardless of whether there's one person or twenty posting.
- A company or software project related user is likely to gain many upvotes in their specific field simply by the power of their name.
This is... Irrelevant. Yes, an official "Microsoft" user would probably do exceptionally well in certain tags, just as John Resig did exceptionally well in jquery... but you might as well argue that Jon Skeet should be hobbled because he's well-known in the C# community. It's a well-known problem with attributed answers, not group accounts.
These are not problems per se, but... the rest of the SO user base is made up from individual users. Seeing group accounts in the reputation leagues, in the top users of every tag and so on feels... odd.
Also irrelevant, since there's no good way to identify a "group account" unless the account owner explicitly admits to being more than one person (see below...) Do you get uneasy whenever you see a user posting under the name of his business?
Also, I am having a hard time seeing group accounts partake in community activities like editing and re-tagging. A company is likely to be active in a number of certain limited tags, and many questions in those tags are bound to be about competing products and technologies. There is a certain potential of friction when the account of Company A cleans up the wording of a question about the merits of a product from Company B.
Ok, I have to give this credence: it is possible that a nefarious organization might put together a cadre of "rep farmers" to build up an account with the intention of abusing privileges to harm their competitors. By posting a massive number of mediocre answers, such an account could conceivably hit the 2K necessary for editing in under two weeks, and then find themselves free to trash the site...
...of course, such an organization would have no motivation to 'fess up to it. We might as well put a "I'm a spammer" checkbox next to the "I'm a group" option, for all the good it'll do. And there's also no point in implementing a separate account type as "punishment" for such users when identified: this is overtly hostile behavior - just ban them!
Implementing a limited account type for group users - a subset of users that may be entirely mythical - would serve only to limit abuse from accounts that have no intention of abusing the site. It might work as a safety-net for a respected organization that wishes to hand login details to the new intern without running the risk of being banned for misguided actions on his behalf... But even this serves only to provide encouragement for a type of account that you're already uncomfortable with.
This is - at best - a counter-productive idea, and at worst, a complete waste of site-developer time. We already require full disclosure from users who are honestly trying to participate without crossing the line into abuse - I see no reason to bend over backwards for users who are not honest.