1) Pondicherry lies just about 150 km (146 km if you take ECR, 161 km if you take NH 45) from Chennai. So it doesn't need a genius to figure out that Pondicherry weather is absolutely same as that of Chennai: hot and very humid!
2) If you thought that Pondicherry is a small fishing town with a laid-back air and lots of French people milling around, sorry you may be in for a surprise. Remember that Pondicherry is capital of a union territory (named Pondicherry and having 4 areas: Pondicherry, Yanam, Mahe and Karaikal), so it is by no means a 'small city' and by no more means with a 'laid back air'! Parts of Pondicherry are reminiscent of its French association but they form a very small part of the town. Yes, the streets in this part are named in French but they have their Indian versions as well and autowala won't know either of them! But frankly this part is so small and so well laid out that you can easily roam around onfoot with a map and reach anywhere from anywhere.
3) Autos are costly. Period. The minimum auto fare is Rs. 40. Try shared autos if you can. If you think you can drive your way around you can get two-wheelers on rent. I can't tell you the street name because I forgot to note that.
4) Aurobindo Ashram is NOT a tourist destination. It is what it says, an Ashram. Go only if you know anything about Maharshi Aurobindo and his teachings. And yes, the ashram dining hall serves only the Ashram guests (don't go there expecting to have a sumptuous breakfast!)
5) Auroville is a great place to visit when in Pondicherry. You get many local busses supposedly going to Auroville but will drop you on the road at a point which is about 8 km from the Matrimandir. You will need to take an auto which will charge Rs. 120 (yes for 8 km!). You can roam around in the Matrimandir campus and shop only if you have deep pockets! Auroville products are supposedly handmade and organic and hence cost a bomb.
6) Shopping in rest of Pondicherry is a great experience. Due to low taxes, things like handicrafts, leather goods (HIDESIGN is Pondicherry based brand!) and textiles are fairly cheap. I recommend a shop named 'Splendour' near the secretariat building for handicrafts. Nehru Road and Mission Road are other shopping destinations.
7) Promenade street is good for roaming around but the adjoining beach (named Serenity or Rocky beach) is not the beach you would like to be at. For that head to Paradise beach, about 8 km from bus stop (where my hotel was!). A 3km boat ride in the Pichavaram backwaters will lead you to Paradise beach which is actually VERY clean and very scenic. Auro beach is another beach where people flock to swim and bathe in the sea.
8) Last but not the least, rather very important, travelling to and from Pondicherry. 'To' part is rather easy. You can get loads of state run buses from CMBT (Chennai Mofussil Bus Terminus), Koyembedu and choose to go by ECR or NH45. Both the roads are extremely good and journey is a breeze. Returning is what makes this point so special! From Pondicherry bus stand, the buses going to Chennai are at particular time slots and you need to take a token for a particular bus. And it can be extremely crowded at the bus stand so don't say you weren't warned!
Go and give time a break in Pondicherry!