Corporations are sponsoring OpenSource projects. Economical reasons aside it gives a good PR, because OpenSource is in fashion these days. But are these projects really open? Sometimes it feels they are not... Sometimes it's just the visibility: source code is open under OSI-approved license, there's a publicly accessible bugtracker, mailing lists and ... that's all. There's no real openness out there.
Business is a selfish thing, and everybody wants to get a benefit. That's normal, and that's one of the reasons behind OpenSource model. Its beleived benefits are wider publicity, larger userbase and better code quality. Usually a big corporation has a small subset of its tool as an OpenSource application, while building a commercially sold and supported toolset on top.
But OS is no silver bullet, and just opening your source can't give you any benefits. To get larger userbase your application simply must be better than alternatives, OpenSourcing, e.g. win95, won't help it become a leader Operating System. The OpenSource market is rather tight nowadays, so having the source released doesn't help much.
To get better code quality it's not enough to have a bugtracker and a cvs server. Project management must have its #1 priority fixing bugs in bugtracker, and not the bugs showstopping some commercial on-top release. Corporate managers tend to have a greater confidence in usability studies and guru recommendations then in plain mailing lists or bugtracker votes, usually being not able to understand that the primary user target group of opesource program is the active user base.
The better publicity is in no way has anything to do with Open Source in my beleif. While OSS is really in fashion, it's just a tiny benefit on a par with website colorscheme. M$ Shared Source initiative is a good example that opening the source code isn't necessarily getting you a strong and positive PR. Larger userbase can probably make a bigger noise, but it can, not must. People are usually talking a lot about what they don't like, and even if the application is great and cures baldness, madness and stuff, the only people who are supposed to mention it are JavaLobby, JDJ, and similiar newsletters. Remember JBoss sertification story. That noise was not user-made but it was planned and implemented by serious marketing talents.
I don't give any recommendations here, because it's very easy to criticize, to be of some use is much much harder...