I’ve been using Gmail for about 5 days now (found out via Evhead about the Blogger offer before the Slashdot story broke) and here are my first impressions:

• The service’s reliability is very good indeed. Even for a beta, this beats Novell’s MyRealbox, and is way better than the other 1 gig free email provider, Spymac.
• Search - Gmail’s strongest pitch - still needs work. “tolkien” fails to match “tolkien’s,” etc. “Silmarillon” does not result in a “Did you mean… Silmarillion” (both of these work in Google’s standard web search). So searching your mailpile isn’t quite as easy as searching the web - yet.
• Being able to access Gmail fully over HTTPS rocks (Go to https://gmail.google.com/ instead of http://…). Myrealbox is the only other free provider that has this, and they are nowhere as reliable.
• Currently you can only store 20 filters. Not quite adequate if you get tons of email.
• Gmail has its own operators for searching email. Some of them are quite nifty, although I would love to have a not operator and a has:responses operator. I expect Google to allow these searches to be carried out through their advanced email search form, since the sheer number of operators may be a bit much for CLI-phobic users.
• It’ll be interesting to see how spamfighters like Suresh treat Gmail when it goes live. Gmail adds no X-Originating-IP, X-Originating-Email or X-Sender header. I wonder if this is Google’s commitment to protecting its users’ privacy, or just an omission in the beta.
• Gmail support informed me that forwarding incoming email to another address is “coming soon”, as is a plain-HTML version of Gmail (the current version is very Javascript heavy, as others have noted, but is probably the most usable webmail interface on the planet.)
• Currently Gmail offers no way to compose HTML email. Not a big problem, but some people may miss it.
• No ads in outgoing email (or in incoming email for that matter). That gets a thumbs up. Many other web email providers, especially Indiatimes (which routinely inserts dating ads into users’ outgoing email), should take note.

Overall, great service so far, and lots of promise. An IMAP interface to non-archived mail (so I could use my favorite MUA) and my happiness would be complete.