The XSi really is all about performance, and boy does it deliver. The engine puts out 100bHP as standard, and mine had a performance air filter and exhaust which probably pushed the power output closer to 120. For a 1.4, the power is remarkable., and the short gearing helps it to a respectable 0-60 time and a top end around the 120mph mark. The XSi's main strength is probably its mid-range. Drop a gear to overtake at 50mph and you'll know all about it.
The wheel-at-each-corner chassis combined with firm suspension give the 106 fantastic handling,. You can throw it about all day, and there's a bit of friendly understeer to warn you when you are getting close to the edge. One thing to look out for though: under extreme cornering, the inside rear wheel can lift off the ground, causing you to make more than one kind of skid mark.
The XSi's practicality perhaps lets it down a bit, for those of you who care about that sort of thing. The seats aren't that comfortable (I used to get cramp in my back on long journeys), and the erratic tick-over and firm clutch make traffic more stressful than it need be. Fuel economy isn't the best either, as the 1.4 lump has to guzzle a fair bit of petrol to put out so much power.
On the whole the XSi is a fantastic car if you do a lot of back-road blasting and not so great if you live in the city. If I move to the country I'll get one again (or maybe it's big brother, the GTi), but for the time being I don't so I'm sticking with something a bit more refined.