I went there a few years ago. Stayed between Sousse and Port El-Kantoui (sp?).
We went on a shoestring budget for a fortnight, but had an amazing time.
Plenty to do around Sousse. The sook is an experience, but look everywhere before buying anything. Haggling is the norm, but always use the prices in the state shop as a guide. Then get it cheaper in the markets.
I found all the hotel and restaurant staff exceptionally friendly. As said before, tip a little (and I mean a little) and you will make their day and receive even better service.
We did the coach tour through El Djem, Matmata then the Sahara. It was a bit rushed in 3 days(and having sunburn on the back of your legs on a coach trip is baaad!), but very interesting.
We also took public transport into Tunis, then on to Carthage for a wander - word of warning - don't stop outside the presidents palace and rummage in your rucksack, ignoring the shouts behind you, then turning around to see you are being charged by bodyguards with well used SMG's
We went quad biking twice, and it was so cheap. The terrain is wonderful for it - olive groves, dusty trails etc.
The beaches are lovely, the sea warm and blue. Your money will go a long way.
The worst thing about Tunisia was that it opened my eyes on how nast camels actually are! Vile, evil creatures hell bent on eating me, glaring at me or spitting at me!