Logging custom error for SharePoint 2010 custom code

Problem: SP2010 has good logging in the ULS logs. Unlike MOSS you can write to the ULS logs in SharePoint 2010, allowing for a single consistant place to log your errors. The event viewer logs errors to a lesser extent than ULS where administrators tend to look first. However, on all projects the topic of how and where to log custom coding errors comes up. What level should the event be caught at and where should they be placed. I have seen multiple was of doing this and it really comes down to what the previous projects used and how do you want to monitor errors.
Tips:

1. Don't write code to function using error catching i.e. I have seen developers catch a specific error and from this position they know the code is to follow specific logic -it's very inefficient. Write code to deal with all situations.
2. Catch errors as specifically as possible, then decide if the error should be bubbled up or can it be dealt with via the logs. But catch the appropriate errors so they are logged.
3. You can write to Unified Logging Service(ULS) logs but these are often not checked or hard to find issues you have thrown up in your code, so consider using a logging block such as Microsoft's Enterprise Logging blocks or Log4net. Ted Pattison suggests writing to ULS and he know his stuff so if you don't have another specified logging policy write to the ULS. And if you do have another logging method consider writing to the ULS anyway.
4. There are a lot of logging applications for .NET, and most companies tend to have logging code ready for implementation on your SP 2010 project.
5. I have seen a MS gold partner use tracing on all projects. So when an error occurs they turn on tracing and try replicate the issue in production environments. Far better to catch errors so you can get your issues resolved quickly and don't need to change config setting or leave tracing enabled on the live production boxes.
6. A web part error can cause an entire page to throw an application error. However don't throw try catch blocks around all code, rather try catch the errors at more appropriate junctions such as at the service layer. Once again it really depends on the WP.

Summary: Avoid using errors for logic (pretty obvious). Log the errors to a distinct area (database, file system(xml files are pretty useful)) to identifying where and what the issue is. Catch specific errors -try not to catch general exceptions and if you do need to catch general exceptions make sure you have looked for more specific exceptions such nullrefobjectexceptions.

More Info:
MSDN SharePoint Logger - http://msdn.microsoft.com/en-us/library/ff798361.aspx
Writing to the ULS
Update: 5 Dec 2010 - Writing to ULS using SP2010 by Waldek Mastykarz
Update: 18 Jab 2011 - MSDN article on logging and debugging

The SharePoint Logger
using Microsoft.Practices.ServiceLocation;ILogger logger = SharePointServiceLocator.GetCurrent().GetInstance();
using Microsoft.Practices.SharePoint.Common.ServiceLocation;
using Microsoft.Practices.SharePoint.Common.Logging;
IServiceLocator serviceLocator = SharePointServiceLocator.GetCurrent();
ILogger logger = serviceLocator.GetInstance();
logger.TraceToDeveloper("Unexpected condition");

Update 14 Dec 2010 - ULS Viewer - Tool to view ULS log and filter data
Update 23 Dec 2010 - Tracing using CorrelationId