You can open different sheets in a workbook but thats about it. I think Docs 2 Go is a pretty robust app but doesnt get close to running like real excel. You will need to save the workbooks in macro/vba free form (so .xlsx) to open them on any of the office apps (even the desktop Mac excel program has abandoned VBA support so i doubt it will ever be moved to the iPad native office suite.) So you will see the printed results of running the code after its done on a Win 7 computer...but you will not be able to edit or work in the VBA environment at all. The tablet apps only support a small set of excel forumulas. If a formla isnt supported only the output of the formula is shown. Further: If your sheet uses formulas that are unsupported (which is all but the basic ones) the sheet opens as read only on Docs 2 go. It may not open at all on other apps...I haven't used them all honestly :-(
Certain formatting don't translate to certain office apps either...like if you are working in ranges your hidden columns/rows come back and those data ponts end up in sums/subtotals etc. Further I cant get any of the big sheets (like over 7500-10000 rows) to even open on iPad. Even on Motorola Xoom, they take a good 3-5 minutes to render and sometimes crash as well if they involve heavy formatting.
Honestly,these functions are probably a bridge too far for tablet excel apps as they are very cpu heavy even on a dual core laptop. That being said, I've had awesome success with working on excel in my remote desktop environment and saving to dropbox and google docs (along with my hard drive at home.) Opening a read only version of a model can sometimes be better than nothing if you are on the fly. Its nice to put calculations physically in someones hand even of they cant see the code the created the final numbers. And with remote desktop you can work with excel remotely on your computer if you are stuck in an airport or something!
While I am massive excel junkie myself and know how dissapointing it is that office apps are limited on tablets...this shouldn't be a reason to hold you back if you have other uses in mind for your tablet. iPad 2 is a nice device that can do a lot and is super convenient...but VBA is prolly not gonna happen.
Sent from my Android 3.1 Motorola Xoom Tablet!