Your hack for IE7 and below really shouldn't be used as it is not valid code.

#block {
margin-top: 5px; /* target only IE8 + Firefox browsers */
*margin-top: 10px; /* target only IE7 and older browsers */
}

Better off with some alternative like *:first-child+html and * html which are valid. It may be a bit of extra code but it its better than code that doesn't validate.

In response to John and Rowan's comments, thank you for your feedback and you do both have valid points about conditional comments. They are great and are one of the best ways to make a site work in all browsers, however these are not always possible to implement.

This post was written more to help people quickly fix bugs on sites that are already built (as this is the task that sparked this blog entry, and the site in questions was not built by ireckon), and to fix for IE8 as there is not always the option to add a new conditional comment into the header for a past project, or someone else's code. Depending on how the site has been built, it is sometimes not possible to simply update the header to add conditional comments, as the site could be quite advanced and could have multiple page templates for example, which cannot be easily updated. Also, spending the time adding all the conditional comments throughout the site, and creating additional style sheets can be time consuming and not possible within a budget.

Conditional comments also have downsides to their uses:
- They add more header calls in the body of the file, which slows down sites, especially if the lag time between requests isn't great, which can be the case for international sites or those that are hosted in the US or offshore. This also is duplicated when you have an [if IE ] and an [if IE 6] for example.
- Using [if lte IE 7] also can cause some problems, in that if you need to fix a bug in IE 6 only you could technically put in a conditional comment using the above, however it would be loaded in 6 and 7, but if you used [if lte IE 7] & [if lte IE 6] they you would get double requests to the server as IE 6 would load both of these. However in this example, it would be better to use [if IE 7] & [if IE 6].

So all in all you also have to be careful of how you use conditional comments and where and how you use hacks, as hacks can sometimes be an affordable option for clients, and can also help with page load.

Personally I think starting a project with conditional comments is the way to go, even if you don't use them. But if it's only a small project or a design that you can build with limited amount of browser bugs, then hacks can be the most efficient way especially if there are only one or two hacks. This will also make it less confusing for updating the site later, as all CSS is located in one file.

You're better off using conditional comments instead if you're only targetting bugs in IE browsers.