I usually just drag tab-sep files into an open Excel window, and it opens just fine. I only get the import wizard when I try to use file -> open. There are a couple of "gotchas" I regularly experience- the worst of which is the automatic formatting- which unfortunately converts a number of gene names into dates (I'm in Bioinformatics). It's enough of an issue that papers have been published about it [1]. For example MAR1 ends up formatted as 1-Mar. When you have a list of 20,000 identifiers, it's quite annoying to deal with. I see the transformed strings show up in biological databases all the time. I don't know why there isn't an easy way to disable autoformatting. Even if I avoid incorporating Excel into my own workflow, when I send documents to scientists, they're going to want to use it, and we end up with the same results then.

[1] http://www.ncbi.nlm.nih.gov/pubmed/15214961