Is there a way for users who have previously filled out a form to select an option that says: “i’m a return visitor” and it will bring back their previous details and then they only need to add in whatever additional details are required for another form? And is it possible to associate values from one form with another?

This is unfortunately not available at this time.

However, depending on your circumstances, it might be worth giving the Weblog Entries SAEF / FormHelper (for editing SAEF) a shot, as surely this would be doable

The situation is it’s a tennis association website where people fill out a registration form at the beginning of the season. Then later they might want to nominate themselves for particular tournaments, but they don’t really need to fill out all their details again; ideally they’d just enter their surname and email address, select their tournament and their previously entered record would then be updated to reflect the tournament they’ve chosen (although it would be better if each tournament was held in a separate table).

I would definately say go with the Weblog Entries route… and incorporate a bunch of conditionals.

You’ll also run in the the problem with only wanting them to post one entry… so have a look here:
http://www.solspace.com/forums/viewthread/313/#2449

If you use weblogs though, can it be incorporated with the way that Freeform stores its entries in a table which can then be exported to Excel, because that’s also one of the main requirements?

I see.... it could probably be done as a manual phpAdmin export… but it probably gets pretty messy at that point.

Yeah, it does. The users of this are pretty non-technical. Just exporting the spreadsheet from Freeform has proved troublesome for them so far. So do I have to choose between normal weblog entries or freeform entries but not combining the two?

Pretty much....

Although Freeform does not allow you to edit the data, so you’re out of luck there.

I’m just curious… why is it that the data needs to be exported in Excel?

If it’s for readability, etc… Why not just offer a “web-based” version (using the regular Weblog Entries tag on a seperate “reports” page).
From this, they can do all sorts of things an Excel Spreadsheet can’t…

Search, Sort, Sift

Because the association admins have been using Excel for this process for a while so it’s the way they’re used to working. It’s going to take them a while to move to a completely different process.

Recreating all this with weblog entries also sounds like it would require quite a bit of work, probably more than they’d want to pay for. They haven’t actually requested the ability for people to retrieve previously entered details - they just want the data captured. It was me who thought it would be better if it could be done this way but it sounds like it’s going to be too involved.