Lack of VMS Standards
One of the most common end user questions is: How do you watch video from multiple DVR/VMS systems in a singular interface? The options are poor, the issue is problematic and it's not being addressed by IP camera standards. See our debate on VMS system standards [link no longer available] in the LinkedIn group [Note: Free registration required].
You have 2 options. (1) You buy third party software (generally called PSIM but the term is debated) that develops support for the proprietary interface of each DVR/VMS. Downsides include: not having support for specific manufacturers, often limited functionalities for reviewing, searching and exporting video and significant cost to implement. Option (2) is to throw out all the equipment except for one manufacturer and 'standardize' on that proprietary solution.
This is great for incumbent manufacturers as customers are reluctant to force their users to use multiple viewing clients (training issues, administrative complexity, confusion about which cameras or sites are viewed on which software). It encourages lock-in.
Is it as big a problem as lack of standards for IP cameras? I am not sure but it is a major factor and problem for many end users.
[Update 2012: While ONVIF has become widespread for connecting IP cameras to VMSes, connecting VMSes remains problemtic. See our tutorial on Recorders integrating with Other Recorders.]