Matt Rogers recently added UPSTREAM as a report resolution type on bugs.kde.org for us. I asked for this because a lot of issues in Plasma were the result of bugs elsewhere in the stack and I hated closing those reports as INVALID since they were not INVALID at all: they just weren't something we could do anything about in the Plasma code base.
Technically not all the bugs we close are really UPSTREAM, though. Some are DOWNSTREAM, namely the bugs caused by packaging foobars or poor backporting decision making and/or execution by OSVs (operating system vendors, aka "distributions" in the Linux realm). However, since we don't have DOWNSTREAM as an option we mark them all as UPSTREAM, noting where in the stack the problem really is in the comments section.
We've only had the UPSTREAM designation for a couple weeks now and already we've closed 19 reports in Plasma as such. That's probably about 10% of reports, which may sound high (and, well, it is) but it's actually a lot lower than it was.
First off, OSVs are actually getting better at packaging Plasma which is leading to fewer problems there. We're also making it easier on them by having fewer interesting Plasmoids in playground and keeping binary compatibility in libplasma while having a symbols check on plugin load (thanks to an upstream, actually; namely Dirk @ OpenSuse). I expect to see an uptick in this category, though, as we're already seeing reports coming in from packages being pushed out with half-baked backports.
Second contributing factor is that the graphics driver issues are actually getting sorted out bit by bit. The newest NVidia driver, for instance, actually works across the board with Plasma. Performance is great (even across multiple screens, apparently) and no artifacts to be seen. They aren't the only ones working successfully through issues, either, and so this area of UPSTREAM bugs is slowly but surefly declining.
Third, bugs in Qt are getting hammered out and fixed. Alexis Menard, who was a student of Kevin Ottens (explaining how he got involved with KDE in the first place =) and a Plasma hacker for the last year and a half or so is now working at Qt Software in Oslo and doing a great job of triaging issues Plasma reveals in QGraphicsView and elsewhere. So that source of UPSTREAM should also be diminishing in the coming months.
As much as it's fun to go "hey, that bug's not our fault! *CLOSE*" it really pains me to mark things as UPSTREAM because it means our software suffers due to bugs in other people's code that I don't work on and therefore have a limited ability to affect positive change in. Working around other people's bugs is sometimes possible .. but a matter of last resort, and completely off the table when it results in a worsened user experience.
For the last year we've really taken it in the proverbial ass over UPSTREAM issues, but it seems that the clouds are finally parting and the sun is shining through. 2009 may actually be a year in which the overwhelming majority of bugs filed against Plasma are actually our own screw ups. =)