What type of budget do you have to invest in a DR solution? There is a growing number of products available using snapshot technology to back up databases such as Exchange or SQL which minimizes gaps between data collection. Open file technology has improved quite a bit as well. Downside to these options are they require a good chunk of available storage to house your snapshot data, constantly running jobs during the course of the work day will most likley place a load on your network performance and the products that are worth their salt are going to come with premium price tags.
The only way I know to truley have up to the second real time backups is to set up a mirror of your Exchange server to a hot spare or VM Exchange server. In larger environments clustering may be a viable option as well.
If your organization is on a budget as most are these days, the chance of losing several hours of data is going to exist. The bright side is that should you completely loose your Exchange server, your still going to be able to recover better than 95% of your data which will keep things running quite smoothly. And should someone need to replace a lost message, it’s far easier to have a contact re-send a message that is 3 or 4 hours old than one that is several days, weeks or even months old.