Take for example two very common plugins that I usually have to deal with for reporting, document management/archive, etc.
PDF plugins (Adobe)
TIFF plugins (variety)
Adobe PDF plugins -
- Versions/upgrades regularly, users have to regular update 'the site', even though it's not the site, it is the plugin asking for upgrades.
- To embed, not embed, dealing with pop-ups allowed.
- And...here is a good one....the web-embed adobe plugin making *multiple* http requests for the same content, and if your logging didn't account for that - multiple logs (see http 206, byte serving/byte range requests).
TIFF plugins -
- Variety of plugins with different options/features/control (and even something 'simple' like if the plugin allows multiple page viewing....apparently not standard?!)
- You, your client/customer, or someone, has Outlook/Office installed and it has an update, a critical update, a security update, whatever -- and reverts to using the MS Tiff viewer by default despite your best effort to use a different TIFF plugin.
- TIFF encoding/compression formats (i.e. g3/fax compression that has an X-Y ratio difference, that some plugins understand and show 'correctly', and others that show without the appropriate ratio and have 'crunched' images).
- And the occasional TIFF that has a byte that isn't understood by Plugin XYZ, or other plugin, but yes on this plugin....search for it, they happen.
Then you add in other plugins like flash/shockwave, java applets, activex/silverlight, codec/encoding video players (whether to use quicktime, realplayer, windows media player, divx, ......), and developers just can not wait until HTML 5 becomes a real-world/real-usage deal.